VMware Real Time Scenario Interview Q & A

Part II

Scenario 31: DNS & Name-Resolution Failures in vSphere Infrastructure

An enterprise virtualization environment running VMware vSphere began experiencing intermittent host disconnects, failed migrations, and sporadic management-UI issues. On investigation the root cause was found to be DNS misconfigurations — missing reverse lookup zones, outdated A/AAAA records, and inconsistent FQDN usage between the vCenter, ESXi hosts, storage arrays and switches.

Symptoms:

Some ESXi hosts show as “Disconnected” or “N

ot responding” in vCenter despite being pingable.

Migration (vMotion/Storage vMotion) or clustering (HA/DRS) tasks fail with errors referencing host identity or network.

Logs contain errors like “Cannot resolve host”, “unexpected host identity”, or “lookup failed”.

Root cause analysis:

The vSphere management stack (vCenter, hosts, storage, clusters) relies heavily on precise name and address resolution. According to troubleshooting guidance, DNS is one of the frequent culprits behind “mystery” behaviours in vSphere.

When forward/reverse records are inconsistent, hosts may not properly join clusters, storage paths may fail, or authentication/management may break.

Troubleshooting steps:

On vCenter and each ESXi host, verify that the hostname (FQDN) is set correctly and matches DNS records.

From each host, run nslookup FQDN and nslookup IP (reverse lookup) to confirm both directions.

Check DNS zones: confirm forward and reverse lookup zones exist, correct entries present, no duplicates.

Review logs on the hosts and vCenter for DNS resolution errors.

For storage/array connectivity and host clustering tasks, verify that all name resolutions succeed.

Solution:

Clean up and standardize DNS entries: ensure each host, vCenter, storage controller has correct A/AAAA and PTR records.

Enforce using FQDN in vSphere configuration (not only IP).

Add alerting/monitoring for DNS resolution failures in the infrastructure.

Include DNS validation check in your pre-upgrade/pre-maintenance checklist.

Scenario 32: Datastore/VMFS Version Mismatch Prevents VM Migrations Post-Upgrade

A data-centre consolidation project upgraded several ESXi hosts to the latest version, but left behind some datastores on older VMFS versions. When administrators tried to migrate VMs between hosts/datastores, tasks failed with compatibility errors. The oversight in matching datastore version to host compatibility caused the migration blockade.

Symptoms:

VM migration or storage migration tasks fail with errors like “Incompatible datastore version” or “Host version not supported”.

Hosts show datastore compatibility warnings in vCenter.

Some VMs may start, but I/O errors occur when moved to older version datastores.

Root cause analysis:

Each VMFS version supports certain host software versions. When hosts upgrade but datastores remain on legacy versions unsupported by the new host version, operations like Storage vMotion or host reads/writes may fail. Compatibility matrix issues often underpin such failures.

Troubleshooting steps:

For each datastore: check the VMFS version in vSphere UI (“Datastore → Details”).

On hosts: check supported VMFS versions and compatibility matrix (via vendor/VMware documentation).

Review migration task logs for explicit version mismatch labels or errors.

Identify any host-datastore pairs where host can’t support the datastore version.

Solution:

Plan to upgrade datastores (or migrate VMs off) so that all datastores are on a supported VMFS version for the host software.

Before adding upgraded hosts, inventory datastore versions and ensure compatibility.

Prevent new hosts from joining clusters unless datastore compatibility verified.

Scenario 33: Management Layer Instability — vCenter Appliance Datastore Full or Storage Issues

The vCenter Server Appliance (VCSA) in a virtualised environment began showing signs of instability: sluggish UI, intermittent service failures, hosts dropping out of management, and vSphere tasks failing. On inspection, the datastore hosting the VCSA VM was nearly full, and logs revealed I/O errors on that LUN. VMware’s KB identifies storage issues for the vCenter VM as a common cause of erratic behavior.

Symptoms:

vCenter UI becomes unresponsive or times out.

Hosts show “Not responding” in the inventory though they are reachable from network.

Logs show file system or storage errors linked to the vCenter VM’s VMFS/datastore.

Root cause analysis:

The management layer is critical: when the VM hosting vCenter suffers storage degradation (full datastore, latency, mis-aligned paths), this cascades to management tasks (host registration, cluster health, vMotion etc.). VMware’s article specifically links vCenter instability with underlying storage LUN issues.

Troubleshooting steps:

Identify the datastore and underlying LUN hosting the vCenter VM (via vim-cmd vmsvc/getallvms, esxcli storage vmfs extent list).

Check free space on that datastore and host logs (/var/log/vmkernel.log, /var/log/vobd.log) for I/O errors.

On the vCenter VM itself (console or SSH), check disk usage (df -h), log volume usage, service statuses (service-control --status --all).

Test host-to-vCenter connectivity; verify storage paths for management traffic.

Solution:

Free up space or expand datastore hosting vCenter VM.

Move vCenter VM to a healthier datastore if needed.

Monitor datastore free space, set alerts when drops below threshold.

Ensure the storage LUN for the management layer has sufficient performance headroom (I/O, latency).

Scenario 34: Legacy Storage Controller Firmware Prevents VM Migration After Host Upgrade

Following an ESXi host software upgrade, a virtualisation team attempted to migrate VMs off older hosts to retire them. But migrations (vMotion/Storage vMotion) began failing with storage path or driver errors. Investigation revealed the storage array’s controller firmware was outdated and not certified for the new host release, blocking migrations and leaving hosts stranded.

Symptoms:

Migration tasks fail with messages about “unsupported driver/firmware” or “migration aborted due to storage path error”.

Host logs indicate SCSI commands failing, path resets, or driver mismatch warnings.

Some VMs show stuck migration states or cannot be powered off for migration.

Root cause analysis:

Host software upgrades must align with storage hardware/firmware capabilities. If storage vendor firmware or host driver versions are not certified for the new host version, features like migration, snapshots, or new virtual hardware may not function correctly. Compatibility lists exist and mismatches cause significant issues.

Troubleshooting steps:

Review migration error logs to identify firmware/driver mismatch messages.

Check storage array vendor compatibility matrix for host version vs firmware version.

On host, via esxcli storage core adapter list or vendor tools, check driver/firmware versions.

Attempt migration of a smaller/trivial VM to isolate if all migrations fail or only heavy ones.

Solution:

Patch or update storage controller firmware and host drivers to certified versions before host upgrade.

In upgrade planning, incorporate storage firmware/driver update phase.

Maintain a hardware/firmware inventory and track compatibility status.

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Scenario 35: VM Sprawl & Idle VMs Causing Resource Waste and Performance Impact

A mid-sized business saw rapid unchecked growth of virtual machines over years. Many VMs were powered on but idle, consumed memory/CPU licensing/backup resources, and contributed to resource saturation. This “sprawl” created unexpected performance bottlenecks for business-critical VMs, as hosts became over-committed with idle-but-on VMs, snapshots, backups and underlying overhead.

Symptoms:

Hosts show high memory usage though guest OSes show minimal CPU/IO activity.

Datastores fill up (snapshot chains, old powered-off VMs still on storage).

Performance of key workloads degrades despite apparent headroom.

Root cause analysis:

VM sprawl means idle or under-used VMs continue to consume resources (memory reservations, snapshots, disk space, backups). These overheads may not be visible but degrade infrastructure. Articles on VMware issues cite improper configuration, resource constraints, and hardware/software mismatches all contributing to performance issues.

Troubleshooting steps:

Inventory all VMs and identify those with low activity (e.g., <5% CPU/IO for past 30 days).

Check snapshot usage/age for these VMs; many snapshots or large delta files indicate hidden cost.

Review resource-pool assignments, reservations, memory limits for idle VMs.

Evaluate cost/licensing impact (powered-on VMs still consuming license counts).

Solution:

Establish a VM lifecycle policy: powered-on idle VMs should be reviewed quarterly, shut down or consolidated if unused.

Deploy monitoring tools to flag idle VMs, large/old snapshots, under-utilised VMs.

Reclaim resources: power off/delete idle VMs, remove stale snapshots, migrate off overloaded hosts.

Track and report resource waste periodically to management.

Scenario 31: DNS & Name-Resolution Failures in vSphere Infrastructure

In a virtualisation setup, hosts began showing intermittent “Disconnected” status in vCenter, migrations failed, HA didn’t kick in. The root was traced to DNS mis-configurations: missing reverse lookup (PTR) zones, inconsistent hostnames between vCenter and ESXi, storage controllers using wrong FQDN.

Symptoms:

Hosts appear healthy on ping but show as “Not Responding” in vCenter.

vMotion/DRS tasks fail with host identity or resolution errors.

Logs show “lookup failed”, “unknown host” or “unexpected host identity”.

Root cause analysis:

Management, clustering and storage features in vSphere rely heavily on name resolution and FQDN consistency. When forward or reverse DNS entries are incorrect—or when hosts use IPs instead of FQDNs—subtle faults arise. According to a troubleshooting guide, DNS issues are a frequent underlying cause in VMware infrastructures.

Troubleshooting steps:

On vCenter + each ESXi host: verify the hostname (FQDN) configured and compare to DNS records.

From each host execute nslookup <vCenter FQDN> and nslookup <host IP> (reverse lookup).

Inspect DNS zones: confirm forward A/AAAA records, PTR records, no duplicates or stale entries.

Review host and vCenter logs for errors referencing lookup or identity issues.

Solution:

Standardize and correct DNS records: ensure every host and service uses proper FQDN, matching DNS.

Update host configuration to use FQDN (not raw IP) in vCenter membership.

Build alerts for DNS resolution failures impacting hosts/storage.

Include DNS validation in every maintenance/upgrade checklist.

Scenario 32: Datastore/VMFS Version Mismatch Prevents VM Migrations Post-Upgrade

During a host-upgrade initiative, some ESXi hosts were upgraded but datastores remained on older VMFS versions. Subsequently, vMotion and Storage vMotion tasks started failing saying “Incompatible datastore version”. The team had overlooked verifying datastore format compatibility.

Symptoms:

Migration/storage-migration tasks fail with messages like “Incompatible datastore version” or “Host cannot access datastore”.

Hosts show warning icons for datastores in the inventory.

Some VMs on older datastores show I/O or access warnings after migration attempt.

Root cause analysis:

Each datastore format (VMFS version) supports specific ESXi host versions. If a host is upgraded and the datastore remains on a format the host no longer fully supports (or features are deprecated), operations like migrations fail. Research guides highlight storage format mismatches as an ongoing risk.

Troubleshooting steps:

For each datastore, check the VMFS version (via ‘Datastore → Summary/Details’ in vCenter).

On each host, check supported VMFS versions (via compatibility matrix or vendor docs).

Review failed migration task logs for explicit version or compatibility errors.

Identify hosts/datastores pairs where version mismatch exists (host supports new version, datastore is old).

Solution:

Upgrade or migrate datastores to versions supported by all hosts.

Prior to host upgrade, inventory datastore versions and build a compatibility map.

Restrict joining of upgraded hosts to datastores until compatibility is cleared.

Scenario 33: Management Layer Instability — vCenter Appliance Datastore Full or Storage Issues

The vCenter Server Appliance (VCSA) started acting unstable: UI slow, services restarting, hosts dropping from inventory. Investigation revealed the datastore hosting the VCSA VM was nearly full and suffering storage path alerts. According to VMware KB, storage issues for the VCSA VM’s datastore commonly cause erratic behaviour.

Symptoms:

VCSA UI response degraded, timeouts or crashes.

Hosts show “Not Responding” though reachable via network.

Logs on host or vCenter show I/O errors or datastore path issues.

Root cause analysis:

The management layer (vCenter) relies on stable storage; if the VM hosting vCenter has storage issues, capacity shortfall, or latency problems, the entire virtualization infrastructure may suffer. White-papers emphasise the need to treat management VMs with same rigour as workloads.

Troubleshooting steps:

Identify the datastore hosting the vCenter VM (via esxcli storage vmfs extent list or vCenter inventory).

On the ESXi host(s) backing that datastore, inspect free space, latency metrics, storage path health.

On VCSA, check disk usage (e.g., df -h), log directories, service statuses.

Inspect host logs (/var/log/vmkernel.log, /var/log/vobd.log) for storage or I/O errors.

Solution:

Free up / expand datastore capacity hosting VCSA VM.

Move VCSA VM to healthier storage if required.

Monitor VCSA datastore free space and latency; set alerts for capacity/IO thresholds.

Include vCenter VM in capacity planning and storage health check processes.

Scenario 34: Legacy Storage Controller Firmware Prevents VM Migration After Host Upgrade

After upgrading ESXi hosts to the latest version, a team attempted to migrate VMs off older hardware but found migration (vMotion/Storage vMotion) tasks failed. Logs referenced unsupported driver/firmware versions. The storage controller firmware was outdated and incompatible with new host software – an oversight in upgrade planning.

Symptoms:

Migration tasks fail with errors like “Unsupported driver/firmware version” or “SCSI command failed”.

Hosts report driver or firmware mismatch warnings; some VM migrations get stuck.

Storage logs show plus path or HBA driver errors.

Root cause analysis:

Host software upgrades must align with storage controller firmware, drivers, and HBA compatibility. Failure to validate storage hardware compatibility leads to migration and I/O failures. One troubleshooting article highlights hardware incompatibility as a frequent root cause.

Troubleshooting steps:

Review migration task error logs for references to firmware/driver mismatch.

Check host storage controller HBA driver/firmware version (esxcli storage core adapter list etc).

Refer to storage vendor/VMware HCL (Hardware Compatibility List) for compatibility between new host version and controller firmware.

Test migration of a simple VM to isolate whether all migrations are impacted or only certain workloads.

Solution:

Update storage controller firmware and host HBA drivers to versions certified for the host version before proceeding with upgrades.

Include storage firmware/drivers in upgrade planning checklist.

Maintain inventory of firmware/driver versions and compatibility status for all critical hardware.

Scenario 35: VM Sprawl & Idle VMs Causing Resource Waste and Performance Impact

In a growing virtual environment, the number of powered-on VMs kept increasing year after year. Many of them were barely used yet consumed memory, storage, backups, snapshots and licensing headroom. As a result, critical hosts ran out of memory/snapshot space, performance degraded and costs increased. The root cause: lack of lifecycle governance for VMs.

Symptoms:

Many VMs showing minimal CPU/IO activity but still powered on.

Hosts reporting high memory usage despite low guest workload.

Datastores filling up due to many VMs + snapshots; backups wind up longer.

Performance of business-critical VMs starts to degrade though infrastructure seems fine on paper.

Root cause analysis:

VM sprawl leads to resource waste (memory, CPU, storage), higher backup windows, complex management, licensing cost and even performance degradation due to overhead. Articles discussing VMware issues list “resource constraints” and “capacity management” among the top challenges.

Troubleshooting steps:

Inventory all VMs and filter for low activity (e.g., < 5% CPU/IO over past 30 days).

Check for old/unused snapshots and powered-on idle VMs.

Review host and datastore metrics: memory allocated vs used, storage consumed by idle VMs, backup windows extended.

Identify which VMs are business-critical vs candidates for decommission.

Solution:

Define VM lifecycle policy: review idle VMs quarterly, power-off or delete unused VMs, remove old snapshots.

Use monitoring tools that flag idle VMs, large/old snapshots, inefficient resource usage.

Reclaim resources: power-down idle VMs, consolidate snapshots, migrate workloads off overloaded hosts.

Report resource waste metrics to management (costs, licensing, wasted compute) to gain buy-in.

Scenario 36: Intermittent Network Connectivity Loss in VMs

An enterprise observed that while most VMs ran fine, some would intermittently lose network connectivity for no apparent reason. When these VMs were migrated to another host, connectivity would often restore, suggesting a host or network path issue. According to a support thread, intermittent VM network disconnects are often tied to underlying network mis-configurations or hardware issues.

Broadcom Community

Symptoms:

VMs unexpectedly lose network connectivity during normal operation, then regain after migration or reboot.

Hosts show minimal network errors, but guest OS logs indicate network adapter drop/pause.

Logs or alerts might show duplicate MAC address warnings, NIC driver issues, or packet drops.

Root cause analysis:

Such intermittent connectivity issues often stem from network layer problems: switches mis-configured, NIC teaming/failover problems, duplicate MACs, or even blade-server fabric issues. On the VMware side, virtual switch port group mis-configuration, mismatched VLAN tagging, or incorrect physical uplink failure detection may be the culprit.

Troubleshooting steps:

On affected VMs: check guest OS network logs for adapter resets or link down/up events.

On host/physical switch: inspect uplink status, NIC teaming, link flaps, duplicate MAC warnings.

Verify virtual switch/port-group config: ensure consistency across hosts (VLAN IDs, MTU, teaming).

Attempt migration of affected VM to a different host or physical uplink path, see if issue follows or stays.

Solution:

Standardize network configuration: ensure VLAN, teaming, MTU, and uplink settings are consistent across all hosts and switches.

Replace faulty NICs or switches if hardware errors/logs support it.

Implement monitoring/alerting on network link flaps, packet drop counters, and duplicate MAC address events.

Document network design and review periodically for changes.

Scenario 37: High Resource Contention in Cluster Leads to Performance Degradation

In a busy virtualised cluster, performance of several VMs gradually degraded over weeks—apps got slower, latency increased, but nothing clearly stood out in CPU/memory utilization charts. A closer look revealed high resource contention caused by overcommit of CPU or memory and noisy-neighbor VMs hogging resources.

Symptoms:

VMs show high latency (application end-user complaints), despite host CPU/memory not fully saturated.

Host performance charts: increased ‘CPU Ready’ times, memory ballooning/swapping.

Resource pools may show imbalanced share/limit settings, some VMs appearing to starve others.

Root cause analysis:

In virtual environments, resource contention (especially CPU Ready time or memory overcommit) is a common root cause of performance issues. A detailed analysis by NAKIVO highlights how memory and CPU overcommitment lead to slower VM performance.

Troubleshooting steps:

On VMs, check metrics for CPU Ready time, memory balloon/swap usage.

On hosts, check overcommit ratios: number of vCPUs assigned vs physical cores, memory assigned vs physical.

Review resource pool settings: reservations, limits, shares; check if any VM has unfair advantage.

Perform migration of VMs to relieve contention and test if performance improves.

Solution:

Right-size VMs: ensure vCPU/vMemory match workload; avoid over-allocating.

Use DRS or host load balancing to distribute workloads evenly.

Set sensible resource pool reservations/limits/shares aligned to business priorities.

Monitor metrics like CPU Ready > 20 ms or memory swap/balloon > X% and alert.

Scenario 38: Backup Jobs Failing After VM Storage Migration

After migrating a large number of VMs to new datastores as part of a storage refresh, the backup administrator discovered that several backup jobs had silently failed or had incomplete backups. During a restore test, missing data and failed snapshot chains were found. The underlying issue: the backup solution wasn’t updated for changed storage paths and the snapshots used by the solution were broken or mis-registered.

Symptoms:

Backup job log entries show “Success” but restore fails; or job shows warnings.

Logs in backup software referencing missing datastore, invalid snapshot chain, “vStorage API error”.

VMs recently migrated/moved appear more frequently in failed/incomplete restores.

Root cause analysis:

Backup solutions integrated with VMware often rely on specific storage paths, snapshot chains and VM-datastore metadata. When VMs are migrated, renamed, or moved to a different storage tier without updating backup configuration, inconsistencies arise causing backup failures. DNS/hosting issues, storage snapshots or changed datastores can contribute too. A troubleshooting guide lists outdated tools, snapshot size/age and memory limits among top issues.

Troubleshooting steps:

Check backup job logs for impacted VMs; verify last successful restore date.

For affected VMs, check Snapshot Manager in vCenter – any large/old snapshots? Are they present?

Review storage migration records and confirm that backup job configurations were updated.

Perform a test restore of an affected VM to validate backup integrity.

Solution:

Implement change-control that any storage/datastore migration triggers backup job review/update.

Include restore tests in backup routine (not only “jobs succeeded” but verify “restores succeeded”).

Monitor snapshot chains, age, size; alert for old snapshots or large deltas.

Maintain documentation aligning storage topology, VM-datastore mapping, backup configuration.

Scenario 39: vSAN Fault-Tolerance Timer Settings Cause Extended Degraded State

A stretched or converged vSAN cluster experienced a drive failure in one disk group. The cluster went into degraded mode. However, the rebuild did not start immediately; it waited the default repair timer. Meanwhile, performance suffered for business-critical VMs. The team had assumed “vSAN automatically repairs instantly”, but did not configure the timer or spare capacity accordingly.

Symptoms:

vSAN Health shows “Absent component” or “Degraded object” for extended time.

VM I/O latency increases; datastore performance drops.

Logs show message about “object repair timer” or “component missing.”

Root cause analysis:

In vSAN, when a component fails, there is a default delay (object repair timer) before rebuild begins—this is to prevent constant rebuilds if host/flap recovery occurs quickly. However, if spare capacity is limited or timer set too high, the cluster stays in degraded state too long and performance suffers. One analysis emphasizes storage/subsystem issues are a common cause of VM performance degradation.

Troubleshooting steps:

Open vSAN health & monitor “object repair timer delay” setting and current rebuild backlog.

Check disk group spare capacity and ensure there is sufficient space to rebuild without impacting production.

Review network latency between vSAN nodes (especially if stretched cluster) and ensure rebuild traffic isn’t saturated.

Verify host logs for component failure or disk errors.

Solution:

Adjust repair timer settings to match your SLA and workload impact (e.g., reduce from default to 15-30 minutes if acceptable).

Design disk groups with adequate spare capacity so rebuilds complete smoothly.

Monitor rebuild traffic and latency; schedule low-impact periods or throttle rebuild if needed.

Review cluster design and host/storage architecture to avoid bottlenecks under failure conditions.

Scenario 40: Patch Management Neglect Leads to Host Instability & Security Exposure

A virtualised infrastructure operator delayed patching ESXi hosts and related firmware, citing “no issues so far”. Over time, host firmware mismatches, NIC/driver mismatches and security vulnerabilities accumulated. Eventually, storage path failures occurred, host time drift became evident, and a vulnerability scan detected an unpatched CVE in ESXi.

Symptoms:

Hosts report driver/firmware mismatches in vCenter.

Time drift on hosts/VMs; some workloads show log warnings about time sync.

Security scan flags hosts with known vulnerabilities (CVE).

Unexpected stability issues: storage path errors, host disconnections.

Root cause analysis:

Patching is not just about security—unpatched firmware/driver/host versions lead to incompatibility, degraded performance, and instability. A blog on the top issues VMware admins face lists “staying current with hardware firmware, bios and I/O device drivers” as a common challenge.

Troubleshooting steps:

Use Lifecycle Manager (or equivalent) to assess host patch/firmware compliance vs vendor/VMware HCL.

Run vulnerability scans on hosts, checking for known CVEs affecting ESXi versions.

Inspect logs for driver/firmware warnings, storage path resets, time drift alerts.

Check host time sync configuration (NTP) and guest OS clock behaviour.

Solution:

Establish a formal patch-management process: schedule regular ESXi/vCenter patches, firmware/driver updates.

Use staging/test hosts before production roll-out; maintain backups/snapshots in case of trouble.

Automate compliance checks and remediation where possible; monitor non-compliant hosts and vulnerabilities.

Document firmware/driver inventory, maintain compatibility matrix, and align upgrade planning accordingly.

Scenario 41: Mis-Configured VMkernel Ports Leading to Storage or vMotion Failures

A virtualised infrastructure had intermittent failures of storage access and vMotion tasks at off-peak times. The root cause turned out to be VMkernel ports for vMotion and storage traffic being configured incorrectly (for example, both on the same uplink or without proper teaming), meaning that when hardware fail-over or uplink changes happened the traffic path broke. A blog on common networking mistakes in vSphere highlights this as a very frequent mistake.

Symptoms:

vMotion tasks fail or hang when uplinks change or NIC fails.

Storage I/O issues when a host uplink fails (VMkernel port for storage on that uplink).

Hosts show connectivity issues to shared storage or network datastores after NIC fail-over.

Root cause analysis:

In vSphere, different types of traffic (management, vMotion, storage, vSAN) should ideally be segregated via dedicated VMkernel ports and uplinks. If multiple traffic types share a single VMkernel port or uplink, you introduce a single point of failure or oversubscription. The blog states: using only the default VMK0 for everything is “a very particular topic … a big deal” in recent forum discussions.

Chris Colotti's Blog

Troubleshooting steps:

On each ESXi host, inspect “VMkernel adapters” in vSphere → Networking → VMkernel ports: verify which traffic each is carrying.

Review uplink usage and teaming/failover settings: ensure that when a pNIC fails, VMkernel ports failover appropriately.

Simulate or check historical occurrences when uplinks changed/fail-over occurred, and correlate with storage or vMotion task failures.

Check logs on ESXi host (vmkernel.log) for “vmk link down” or “vmk traffic lost” or storage path errors tied to VMkernel port changes.

Solution:

Implement dedicated VMkernel ports for each traffic type (management, vMotion, storage, vSAN if applicable) and assign dedicated uplinks or failover groups.

Configure teaming/failover so each VMkernel port uses a distinct active/standby uplink pair, avoiding overlap.

Use best-practice design: separate physical NICs or logical segmentation for critical traffic types.

Monitor uplink status and VMkernel port failover events; alert when a non-active uplink becomes active for a critical VMkernel port.

Scenario 42: Outdated VMware Tools / Virtual Hardware Causing VM Functionality Loss

In a large virtual environment, administrators discovered that some VMs were missing the latest version of VMware Tools, and a subset was still on older virtual hardware version compatibility. Over time, these VMs exhibited guest OS driver failures, degraded performance, inability to suspend/resume, and lacked new features. A white-paper on common VM issues lists outdated tools/hardware version as #1.

Symptoms:

Guest OS complains of missing drivers or has generic device entries in device manager (Windows) or dmesg (Linux).

VM Tools status shows “Out of date” in vSphere summary tab.

Virtual hardware version is older than the host version; some features disabled or blocked.

Backups or other automation fail due to unsupported hardware version.

Root cause analysis:

VMware Tools provide the integration between guest OS and hypervisor—timing, drivers, paravirtual devices. If missing or outdated, performance and manageability suffer. Similarly, the virtual hardware version defines the capabilities of the VM (vCPU, memory, devices). Upgrading hosts but leaving VMs on legacy hardware version breaks compatibility or blocks features. The white-paper states this is “the most common issue” in virtualised environments.

Troubleshooting steps:

In vCenter, list VMs with Tools status “Out of date / Not installed”.

For VMs showing problems, check virtual hardware version vs host compatibility (in Summary tab).

In guest OS, inspect for driver issues, missing device entries, network/performance degradation.

Check automation tasks (backup, monitoring) logs for errors referencing hardware version or Tools.

Solution:

Establish a maintenance process: upgrade VMware Tools soon after host upgrades, then schedule virtual hardware version upgrades in controlled batches.

For each VM, validate guest OS driver compatibility before upgrading virtual hardware version.

Use inventory/automation to flag VMs with outdated Tools or legacy hardware version.

Document compatibility matrix for your hosts, Tools version, guest OS version, and virtual hardware version.

Scenario 43: Improper Storage Tiering Policy in vSAN or Traditional Storage Resulting in Performance Drops

An organisation deployed automated storage tiering to move “cold” data to slower drives and keep “hot” data on fast SSD/NVMe. However, some business-critical VMs began showing high I/O latency. Investigation revealed that the tiering thresholds were too aggressive and “hot” data had been moved to slower tier drives while the tiering engine was itself consuming I/O bandwidth. Monitoring guidance for vSphere emphasises storage latency as a primary metric to watch.

Symptoms:

Periodic spikes in VM I/O latency, especially on disks/datastores expected to be low-latency.

Storage tiering logs show frequent data movement during business hours.

Storage monitoring shows slow tier drives servicing unexpected workloads.

Root cause analysis:

Automated tiering systems rely on accurate policy definitions and system capacity. In virtualised environments, the “I/O blender” effect (many mixed I/O streams) aggravates performance if data moves unexpectedly. Storage latency is typically the hardest to fix in vSphere.

If tiering mis-classifies data or runs during peak hours, it hurts performance rather than helps.

Troubleshooting steps:

Monitor storage performance metrics: datastore latency, queue depth, IOPS, especially on slower tier drives.

Review tiering logs/policies: thresholds for promotion/demotion, timing of data movement, volume of movement during business hours.

Map VMs impacted to tiered storage: which VMs ended up on slower tier drives unexpectedly?

Check if background tiering tasks coincide with business workload spikes.

Solution:

Rework tiering policy: define realistic thresholds for “hot” vs “cold”, schedule movement during off-peak hours.

Ensure hardware tiers are properly sized: fast tier must handle “hot” workloads; slower tier must not be used for critical VMs.

Monitor tiering outcomes and adjust policy over time.

Add alerts for latency thresholds exceeding safe limits for business workloads.

Scenario 44: Backup/Replication Integration Breaks After Datastore Migration or Rename

After migrating dozens of VMs to new datastores (as part of storage refresh), the backup and replication routines continued to report “success”. However, a restore test revealed missing data and failed snapshot chains. The backup solution logs referenced datastore IDs mismatching what it expected. A blog on common VMware issues lists “storage mis-configuration” and “snapshot/sprawl” as frequent causes.

Symptoms:

Backup job logs show success but restore fails or data is incomplete.

Logs show “snapshot chain missing” or “datastore not found” or “vStorage API error”.

VMs recently migrated/datastore renamed show disproportionate backup/restore issues.

Root cause analysis:

Backup solutions for vSphere rely on consistent datastore identifiers, snapshot chains, and target metadata. When storage changes (datastore rename, migration, path change) occur without updating backup configuration, jobs can silently succeed but not actually protect data properly. The blog article on common VM issues highlights mis-config and hardware compatibility as top risks.

Troubleshooting steps:

Inspect backup/replication logs for impacted VMs, last successful backup timestamp, error/warning details.

For those VMs, open vSphere, check snapshot manager and datastore mapping for the VM.

Review storage migration records to identify renames/moves of datastores, and verify whether backup config was updated accordingly.

Attempt restore of affected VM to validate actual data integrity.

Solution:

Establish strong change-control process: any storage/datastore change must trigger backup configuration review and test restore.

Supplement health of backups with periodic restore testing (not just job success).

Monitor snapshot chains, age, size, and datastore changes; alert if mismatch between backup config and actual datastore mapping.

Document mapping between VM/datastore/backup job and regularly audit.

Scenario 45: Patch Management Neglect Leads to Host Instability and Security Exposure

An IT team postponed applying ESXi and vCenter patches citing risk of downtime. Over months, hosts fell behind: firmware/driver mismatches, storage path resets, time-drift, and a vulnerability scan flagged hosts with known critical CVEs. Eventually, a storage controller bug triggered I/O path failures and a host became unstable. A blog on performance monitoring emphasises that storage issues are often root causes but neglecting hardware/firmware patching exacerbates them.

Symptoms:

Hosts display driver/firmware mismatches in vCenter.

Hosts show time drift or NTP issues; guest OS adverts high latency.

Logs show storage path resets, HBA driver errors, host disconnects.

Security scans flag ESXi hosts with known vulnerabilities.

Root cause analysis:

Patch management isn’t just about security – it’s about driver/firmware compatibility, performance stability, and longevity of the virtual environment. Delayed patches lead to mismatch between host software, firmware, drivers, and storage/hardware, which can trigger performance/availability issues. The performance monitoring article states storage is “the most common bottleneck” – but underlying firmware/driver issues may be the real root.

Troubleshooting steps:

Inventory hosts: check patch levels, firmware/driver levels via Lifecycle Manager or vendor tools.

Run vulnerability scan of hosts for known CVEs; flag non-compliant hosts.

Review logs for storage/controller errors, time sync issues, driver warnings.

Validate NTP sync on hosts and guest OS clocks.

Solution:

Implement patch-management process: schedule updates for ESXi, vCenter, host firmware, drivers, storage controllers.

Use test/staging hosts prior to production rollout, maintain snapshots/backups before patch window.

Automate compliance checking and alert on non-compliant hosts or outdated drivers.

Maintain firmware/driver inventory and compatibility matrix for host and storage hardware.

Scenario 46: Ghost Snapshots Consuming Datastore Space

An environment seemed to have ample free space on its datastores, yet performance of some VMs degraded, and hosts started showing storage alert events. On investigation, administrators found “hidden” delta snapshot files (not visible in the VM’s Snapshot Manager) consuming large volumes of space, causing datastore fills and I/O queuing. As one guide notes: snapshot age and size are among the most common VM issues.

Symptoms:

Datastore free space drops unexpectedly though no new VMs/large files seem active.

“Needs consolidation” warnings for VMs, or snapshot delta files present though no snapshots shown.

VM I/O latency increases, hosts show storage queue backs up.

Root cause analysis:

Snapshots in VMware environments, when not properly managed, grow in size or get “orphaned” (delta files remain even after removal). These ghost snapshots can fill datastores, cause I/O issues, and degrade performance. The “I/O blender” effect worsens when storage is under pressure.

Troubleshooting steps:

Scan datastores for large *-delta.vmdk files or orphaned snapshot files.

In vCenter, check each VM’s Snapshot Manager for hidden snapshots or consolidation needs.

Review datastore free space trend: is free space steadily dropping?

Review host logs for storage latency, “consolidation needed” warnings, or datastore full events.

Solution:

Consolidate or delete snapshots: use Snapshot Manager → Consolidate if “needs consolidation”.

Implement governance: limit snapshot age (e.g., < 48 h) and size (< X GB) per VM.

Monitor datastore free space and delta file sizes; alert when thresholds exceeded.

Avoid long-lived snapshots used as “backup” substitute; educate teams.

Scenario 47: Host Boot Disk Filling Up Causing Host Instability

A host in a VMware cluster started crashing recurring over weeks. On deeper inspection, the root cause turned out to be the ESXi boot disk (USB or SD card) used by the host had filled up with logs, crash-dump files and core files— eventually causing ESXi to hang or become unresponsive. A troubleshooting guide underscores that hardware and driver issues (including boot media) are common culprits.

Symptoms:

Host becomes unresponsive or shows PSOD (Purple Screen of Death) intermittently.

The host’s DCUI shows disk full or logs cannot be written.

Logrotate or VMkernel logs indicate “no space left on device” for boot media.

Root cause analysis:

In many vSphere setups, ESXi runs from a minimal boot device (USB/SD). Over time, logs, scratch, core dumps build up, especially if persistent scratch isn’t configured. When the boot device fills, ESXi cannot function properly—leading to instability or crash.

Troubleshooting steps:

On the host, check /scratch or boot media space via CLI (vdf -h).

Review logs for “write failed” or “no space left” errors.

Check whether persistent scratch is configured and whether logs are spooling to a datastore vs boot media.

Check if host is storing core dumps on boot device and whether those have grown large.

Solution:

Configure persistent scratch location on shared datastore rather than boot device.

Periodically clear old core dumps and logs stored on boot media.

Use sufficiently sized boot media (even if USB/SD) and treat it as critical infrastructure.

Monitor boot device usage; set alert when usage > X%.

Scenario 48: VM Escape Risk via Mis-Configured Nested Virtualization

In a test environment, administrators enabled nested virtualization (running ESXi inside ESXi VM) to test upgrades. Later, they accidentally left the configuration in production inadvertently—allowing a VM to run virtualization features. A security audit flagged this as a VM escape risk because layered hypervisors expand attack surface. A list of common errors in VMware includes configuration errors & drifts.

Symptoms:

VM has vhv.enable = “TRUE” allowing nested virtualization.

Security scan shows hypervisor related flags or anomalous VM privileges.

Unexpected workloads exist inside nested VMs; path to host escalation.

Root cause analysis:

Nested virtualization enables guest VMs to participate in virtualization operations — potentially giving malicious actors ways to access host-level functions if mis-configured. Configuration drift (test settings left in prod) and inadequate controls increase risk.

Troubleshooting steps:

Identify VMs where nested virtualization is enabled (VM > Edit Settings > CPU > Expose virtualization to guest OS).

Review VM and host configuration: is nested support needed? Was it enabled temporarily for dev/test but left active?

Run security audit: check for elevated privileges inside guest VMs, unusual VM capabilities.

Review logs for access or privilege changes in guest VMs.

Solution:

Disable nested virtualization for production VMs unless strictly required.

Establish configuration baselines and drift detection; ensure test/dev settings don’t leak to prod.

Incorporate security controls: restrict hypervisor features, apply least-privilege, monitor nested configuration changes.

Scenario 49: Mis-Sizing vCPU Leading to High CPU Ready Time & Latency

In a consolidation push, administrators increased vCPU allotment per VM (giving VMs more vCPUs “just in case”). After the change, several VMs reported high CPU Ready times and users complained of slower applications even though host CPU usage looked “normal”. A common troubleshooting article lists high ready times as a key performance problem.

Symptoms:

VM performance degraded even though host CPU load isn’t fully saturated.

In VM performance charts: CPU Ready time spiking or abnormally high (e.g., > 10-20% of CPU time).

Resource scheduling delays visible in vCenter metrics.

Root cause analysis:

Over-allocating vCPUs increases scheduling complexity: the hypervisor must schedule each vCPU on a physical core. Too many vCPUs per VM (especially if workload doesn’t use them) leads to increased scheduling wait (“ready time”) and thus latency—even if CPU looks free.

Troubleshooting steps:

In vCenter, monitor VM’s CPU Ready metrics (Advanced charts or Performance tab) and note values.

Check vCPU allocation vs actual used load (inside guest OS via Task Manager/Top).

Review host and cluster: how many vCPUs vs physical cores? Are many high-vCPU VMs on one host?

Consider migrating the VM to a less populated host or reducing vCPU count and monitoring response.

Solution:

Right-size VMs: allocate vCPUs based on workload, not “just in case”.

Use monitoring to identify under‐used vCPU allotments and reduce accordingly.

Balance high vCPU VMs across hosts; use DRS to spread load.

Set alert thresholds for CPU Ready time (e.g., > 20 ms or > 5% of scheduled time) and investigate.

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Scenario 50: Licensing Drift – Hosts Running Unsupported Editions Causing Features Break & Audit Failures

An organisation’s virtual infrastructure grew organically over years. Some hosts had been added under one licensing edition, others under a lower edition. After a version upgrade and audit, they discovered several hosts were running unsupported features (e.g., Distributed Switch, Host Profiles) because of license edition mismatch. The mismatch caused features to stop working and exposed the company to audit penalties. A troubleshooting article lists configuration errors & licence/edition mismatches as high-impact issues.

PivIT Global

Symptoms:

Features disappear or stop working post-upgrade (e.g., DRS, vMotion not available on some hosts).

Licensing screen in vCenter shows warnings about unsupported features or eval mode expiry.

Audit report flags hosts using higher-edition features without license coverage.

Root cause analysis:

License edition drift (some hosts licensed under Standard, others under Enterprise) plus upgrades that require higher edition features lead to functional breaks. Enterprises often forget to align host licence edition with cluster/feature set.

Troubleshooting steps:

Inventory all hosts: check license edition assigned in vCenter (Cluster → Configure → Licenses).

Review feature usage: which features (vMotion, DRS, HA, Distributed Switch) require which editions?

Check audit logs or licensing reports for usage of unsupported features.

If an upgrade was done, confirm that the license edition was upgraded accordingly.

Solution:

Align all hosts to the correct license edition that supports required features.

Use change control: any upgrade or addition of features must include license review.

Generate periodic license usage reports and ensure compliance.

Communicate with management about cost/licensing risk vs feature benefit.

Scenario 51: Boot-Media Saturation on ESXi Hosts Causing Instability

In a datacenter, one ESXi host began showing intermittent host-disconnects and one eventual PSOD (Purple Screen of Death). The operations team discovered that the host was booted from a USB/SD card and the “/scratch” partition and logs had grown until the boot media was full. The saturated boot media caused ESXi services to fail and eventually the host became unstable.

Symptoms:

Host shows “Not Responding” or “Disconnected” in vCenter while network/compute appear fine.

PSOD or host crash pointing at storage or log file errors.

On host console (vdf -h), the boot device (USB/SD) shows near 100 % usage.

Logs in /var/log/vmkernel.log or /var/log/vobd.log show “write failed”, “no space left on device” errors.

Root-cause analysis:

Many ESXi hosts run from small boot devices (USB stick, SD card). They rely on shared datastores or scratch partitions for logs, but if configuration isn’t correct and logging accumulates on the boot device, it can fill. Once the boot medium is full, essential ESXi services may fail. Hardware / driver / firmware issues exacerbate the risk. This aligns with “hardware incompatibilities / resource constraints” as major issues in VMware environments.

Troubleshooting steps:

Login to host shell (or via DCUI) and run vdf -h to check disk usage of boot device and scratch partition.

Inspect logs in /var/log for “no space left” or similar errors.

Check host configuration: whether scratch location is on a shared datastore or stuck on USB/SD device.

Examine recent changes: large log dumps, core-dumps stored locally, large number of powered-off VMs’s snapshots on the same host.

Solution:

Configure persistent scratch on a shared datastore (with sufficient free space) rather than default USB/SD boot media.

Clear old logs, core dumps, and any large files on boot device; ensure boot media usage stays under safe threshold.

Regularly monitor boot device usage and set alerts (e.g., > 80% usage).

Use larger or more reliable boot media if USB/SD is the only option—treat it as part of critical infrastructure.

Scenario 52: Mis-Configured VMkernel Ports for Storage/Vmotion Causing Migration & I/O Failures

A virtualised cluster experienced intermittent migration failures (vMotion/Storage vMotion) and elevated storage latency on one host during uplink failovers. On investigation the admin found that the VMkernel ports for vMotion and storage traffic shared uplinks and lacked redundancy. When a NIC failed or team fail-over occurred, VMkernel port lost path, causing migration failures and storage I/O disruptions.

Symptoms:

vMotion tasks fail mid-way with errors like “Host not accessible for migration”.

Storage latency spikes on a host during uplink-failover events.

Logs show VMkernel link down events tied to storage VMkernel IDs.

Host shows fewer active uplinks than configured for certain VMkernel ports.

Root-cause analysis:

In VMware environments, separating traffic types (management, vMotion, storage, vSAN) via dedicated VMkernel ports and uplinks is best practice. When multiple traffic types share the same uplink or failover group, a single hardware event can affect critical traffic. Network mis-configuration is repeatedly cited among top VMware issues.

Troubleshooting steps:

Go to host → Networking → VMkernel adapters; check each adapter’s “Enabled services” (e.g., vMotion, vSAN, Provisioning).

Check the associated uplinks/active standby for each adapter; verify no overlap of storage and vMotion traffic on same physical link.

Review host logs (vmkernel.log) for “vmk link down” or uplink failover events corresponding to migration failures.

Simulate or review past uplink failures and correlate with migration/storage failure events.

Solution:

Create separate VMkernel ports for storage, vMotion, management; assign distinct uplinks/teaming groups.

Ensure each uplink has sufficient physical NIC capacity and redundancy (active/standby).

Use stricter network design: dedicated physical NICs for critical traffic where possible.

Monitor VMkernel link status and uplink failover events; alert when critical traffic loses primary path.

Scenario 53: Licensing Edition Drift Leading to Feature Loss & Audit Risk

A service-provider environment had added hosts and clusters over years. Some hosts were under one license edition (Standard), others only licensed for Essentials. After an upgrade, it turned out that features like Distributed Switch, vMotion and HA were no longer available on hosts with incorrect license edition. The audit also flagged ineligible feature usage. The result: functionality loss and licensing liability.

Symptoms:

Features previously present (vMotion, DRS, HA) become unavailable on some hosts.

vCenter Licensing view reports unsupported features in use or hosts under evaluation mode.

Audit flagged usage of advanced features without proper license edition.

Cluster warnings about “feature not supported in current license”.

Root-cause analysis:

License edition drift (when hosts and clusters lose sync with license features) is often overlooked. Administrators assume license remains valid and feature set continues. But if hosts run features beyond their licensed edition, after an upgrade they may lose functionality or face audit consequences. The “top issues” list for VMware admins includes licence/edition mismatches.

Troubleshooting steps:

Go to vCenter → Administration → Licensing → Licenses to list all hosts and their assigned license edition.

Cross-check which features are used: e.g., vMotion, DRS, Distributed Switch and map them to host license edition.

Check audit logs or license usage reports for hosts running unsupported features.

For hosts flagged, attempt a feature (e.g., vMotion) to trigger the warning and capture the message.

Solution:

Align hosts to correct license edition matching required features; upgrade license if needed.

Set quarterly/license review process to ensure host cluster license compliance.

Update change-control: any new host/upgrade must include license edition validation.

Regularly generate license usage reports and compare against feature consumption.

Scenario 54: Nested Virtualization Left Enabled in Production Leading to Security Exposure

A team enabled nested virtualization on a cluster to run ESXi in VMs for testing. Later, some production VMs migrated to that cluster with nested virtualization enabled (vhv.enable = TRUE). A security review discovered this mis-configuration exposed the underlying host to potential VM escape vulnerabilities, given that nested hypervisor features were running on production hosts.

Symptoms:

VMs have advanced CPU settings allowing nested virtualization; this option should be disabled in production.

Security scan flags hosts or VMs with nested virtualization enabled.

Strange or unusual VM templates with virtualization features exposed to guests.

Compliance reports indicate mis-configuration in hypervisor capability exposure.

Root-cause analysis:

Nested virtualization is useful for labs/test but introduces increased risk in production: guest OS gets closer to hypervisor layer, increasing attack surface. Mis-configured environments where nested capability is not disabled pose serious security exposure. Configuration drift and failure to revert test settings are common root issues.

Troubleshooting steps:

List all VMs where “Expose virtualization to guest OS” is enabled.

Cross-check cluster/host where nested capability is not needed for workload.

Run security scan or audit for nested virtualization usage.

Check jump-VMs or malware detection: nested features can be exploited.

Solution:

Disable nested virtualization (vhv.enable = FALSE) in production VMs unless explicitly required.

Apply configuration baseline policies to disallow nested virtualization in prod clusters.

Conduct periodic audits of VM compatibility and advanced CPU settings.

Ensure hosts and clusters are hardened: disable unneeded virtualization features, apply least-privilege.

Scenario 55: Ghost / Orphan Snapshots Filling Datastore & Causing Storage Latency

In a virtual environment, datastore free-space started decreasing but no new data seemed to be added. Performance of many VMs declined and storage I/O latency increased. On investigation, large “*-delta.vmdk” files were discovered even though the VMs’ Snapshot Manager showed no snapshots. The cause: orphaned snapshot deltas (ghost snapshots) remaining after deletion, causing hidden disk growth and I/O delays.

Symptoms:

Datastore free space dropping unexpectedly.

VMs show “Needs Consolidation” status though no visible snapshots.

Alarms or logs about datastore nearing capacity or I/O queue depths rising.

Storage path latency high for VMs on that datastore.

Root-cause analysis:

Snapshots that are deleted but not properly consolidated leave behind delta files which still consume space and degrade performance. The “age & size of VM snapshots” is cited among common VMware issues.

Because virtual workloads generate I/O mix (“I/O blender effect”), these latent snapshot delta chains can cause major latency.

Troubleshooting steps:

Scan datastore for large files named *-delta.vmdk or *-redo.vmdk; compare with VMs’ Snapshot Manager view.

In vCenter, check for “Needs Consolidation” status on VMs.

Verify datastore free space trends and check for unexpected consumption.

Review host logs for warnings about snapshot chain or consolidation issues.

Solution:

Force-consolidate snapshots for affected VMs: right-click VM → Snapshot → Consolidate.

Implement snapshot governance: set retention (e.g., no snapshot older than 48 hrs, size < X GB) and automate alerts for breaches.

Regularly run inventory/reporting for orphaned snapshot chains and free space consumption.

Educate teams: snapshots are not backups and should not be permanent.

Scenario 51: Boot-Media Saturation on ESXi Hosts Causing Instability

On one of the ESXi hosts in a cluster, administrators noticed recurring instability and even a Purple Screen Of Death (PSOD). It turned out the host was booted from a USB / SD card and logs, core dumps, and scratch data had filled the boot device. With the boot-media saturated the host services started failing intermittently.

Symptoms:

Host shows “Not Responding” or “Disconnected” in vCenter despite intact network.

Console of the host indicates “no space left” or inability to write logs.

On shell: vdf -h shows boot device near 100% capacity.

Logs show entries like “write failed” or “scratch partition full”.

Root cause analysis:

ESXi hosts often boot from minimal devices (USB/SD) with limited write capacity. If scratch/log partitions aren’t properly directed to shared datastores, the boot device can fill up over time. A host running out of boot-media space becomes unstable. This ties into the general category of “resource constraints / hardware incompatibilities” flagged in VMware issue summaries.

Troubleshooting steps:

Connect via shell / DCUI and run vdf -h to check usage of boot media and scratch locations.

Inspect host logs (/var/log/vmkernel.log, /var/log/vobd.log) for “no space left” or core dump growth.

Check configuration: is scratch location set to boot-media or to a datastore?

Determine if large core dumps or logs are being stored locally, and if automated tasks are writing to boot device.

Solution:

Configure persistent scratch on a shared datastore (not the USB/SD) so logs and temporary files don’t fill limited boot media.

Clear old core dumps/logs on the boot media and monitor free space.

Set monitoring/alerts for boot-device usage (e.g., > 80% fill).

Document boot-device health as part of host-maintenance process.

Scenario 52: Mis-Configured VMkernel Ports for Storage / vMotion Causing Migration & I/O Failures

A cluster saw intermittent vMotion failures and spiking storage I/O latency when some uplinks were failing. On inspection it was discovered that VMkernel ports used for storage and vMotion were sharing the same uplink or had insufficient redundancy. When a NIC or uplink failed, the storage or migration traffic path was disrupted.

Symptoms:

vMotion tasks fail mid-flight or hang.

On a host, storage latency spikes or datastore becomes inaccessible after uplink failover.

Logs show VMkernel link-down events corresponding to VMkernel adapters used for storage/vMotion.

Root cause analysis:

VMkernel adapters carry specific traffic (vMotion, storage, management, vSAN)—if uplinks are shared or not properly segregated, a failure in one physical path can disrupt major services. A known “most common networking mistake in vSphere” is insufficient VMkernel traffic separation.

Troubleshooting steps:

Review Host → Networking → VMkernel Adapters: check each adapter’s services and uplink assignments.

Identify if vMotion/storage VMkernel adapters share uplinks with other traffic or lack active/standby NICs.

Check uplink failover events in logs (vmkernel.log) and match to migration or I/O failures.

Possibly simulate uplink failover (during maintenance window) to test redundancy.

Solution:

Create dedicated VMkernel ports for storage and vMotion, each with distinct uplink groups/teaming.

Ensure failover settings and active-standby uplinks are correctly configured.

Monitor uplink status, failover events, and link usage for these VMkernel adapters.

Scenario 53: Licensing-Edition Drift Leading to Feature Loss & Audit Risk

In a multi-cluster environment, over time new hosts were added, some upgraded, and licencing tracking lagged. After an upgrade, the team noticed some features (Distributed Switch, vMotion) stopped functioning on certain hosts. On audit the licensing didn’t align with the features used.

Symptoms:

Some hosts no longer have certain features active (vMotion/DRS) though they formerly did.

vCenter Licensing view shows hosts under basic licence edition despite using advanced features.

Audit report flags unsupported feature usage or eval periods.

Root cause analysis:

License edition drift happens when features are assumed but not tracked. When upgrades or configuration changes occur, mismatch between host licence edition and enabled features cause functional loss and compliance risk. Licensing/edition mismatch is among top-reported VMware issues.

Troubleshooting steps:

In vCenter → Administration → Licensing → Licenses: list each host and its assigned licence edition.

Check which features are actively used (vMotion, DRS, distributed switches) and map to licence edition requirements.

Review recent changes/upgrades – did any host join cluster requiring advanced licence but still had lower edition?

Check for audit logs or alerts in vCenter about licence non-compliance.

Solution:

Align host licences with actual feature usage; upgrade licence if needed.

Implement periodic licence audits and tracking of edition usage.

Integrate licence review in upgrade/change control processes.

Scenario 54: Nested Virtualization Left Enabled in Production Leading to Security Exposure

A lab environment enabled nested virtualization (ESXi in VM) for testing. Later VMs with nested settings were migrated to a production cluster inadvertently. A security review revealed that exposing nested virtualization in production increases attack surface (VM escape risk) and configuration drift had let it happen.

Symptoms:

Some VMs have CPU settings “Expose virtualization to guest OS” enabled.

Security scan flags hosts/VMs with nested virtualization enabled.

Unexpected VMs running nested workloads on prod cluster.

Root cause analysis:

Nested virtualization is powerful for test/dev but risky in production: guests gain hypervisor-level capabilities, possibly enabling VM escape or privilege elevation. Configuration drift (test settings leaking into production) is a common issue.

Troubleshooting steps:

Inventory VMs with nested virtualization enabled (vmx setting vhv.enable = “TRUE”).

Check clusters/hosts meant for production for nested settings.

Run security audit or scan for hypervisor-capability exposure.

Review change control logs for test settings migrating to production.

Solution:

Disable nested virtualization in production VMs unless explicitly required.

Configure baseline/hardening standards preventing nested settings in prod.

Include nested-setting audit in regular security/objective reviews.

Scenario 55: Ghost / Orphan Snapshots Filling Datastore & Causing Storage Latency

A datastore’s free space was steadily decreasing though no large workloads had been added. Ultimately VM performance degraded due to storage latency. Investigation found large delta-VMDK files—snapshot deltas no longer visible in snapshot manager (“orphan snapshots”). The hidden snapshot chain caused I/O queuing and free space erosion.

Symptoms:

Datastore free space drops unexplained.

Many VMs show “Needs consolidation” though no snapshot recorded.

Storage latency spikes on datastores hosting the deltas.

Root cause analysis:

Snapshots, when not properly managed or consolidated, leave delta files that still incur I/O overhead. Over time, this hidden overhead (plus free-space consumption) causes performance issues. Snapshot age/size is frequently cited among common VMware issues.

Troubleshooting steps:

List large files on datastore matching *-delta.vmdk, *-redo.vmdk that don’t correspond to visible snapshots.

In vCenter, check VMs for “Needs consolidation” or unresolved snapshots.

Review free-space trend on datastore; correlate to performance degradation.

Host logs: see “consolidation needed” warnings or storage queue latency.

Solution:

Consolidate snapshots for affected VMs: take snapshot manager → consolidate.

Set policy: snapshots should not be older than X hours/days, size limited.

Monitor for orphan deltas and alert when delta files found.

Scenario 51: Boot-Media Saturation on ESXi Hosts Causing Instability

In a production cluster, one ESXi host began showing recurring instability and eventually a Purple Screen of Death (PSOD). After investigation, the team discovered the host was booted from a small USB/SD card, and the host’s scratch/log partition had filled up, causing services to fail.

Symptoms:

Host shows “Not Responding” or “Disconnected” in vCenter despite network connectivity.

Console shows error about disk full or writes failing.

On the host CLI, vdf -h shows boot device usage at nearly 100%.

Log entries show “no space left on device” or “scratch partition full”.

Root cause analysis:

Many ESXi hosts use USB/SD boot media which have limited write endurance and space. If logs, core dumps or scratch files accumulate there (especially if persistent scratch isn’t configured), the boot device can saturate, causing host instability. This kind of hardware/boot-device issue falls under “hardware incompatibilities / resource constraints” (see general VMware issues summary).

Troubleshooting steps:

On the host, via the shell or DCUI, run vdf -h to check disk usage of boot media and scratch partitions.

Inspect /var/log/vmkernel.log, /var/log/vobd.log for errors about writes failing or no space left.

Check if persistent scratch is configured on a shared datastore instead of boot media.

Review recent changes: were there large core dumps generated, or are logs configured to dump locally on boot media?

Solution:

Configure persistent scratch on a shared datastore (instead of USB/SD boot device) so host logs and scratch files don’t fill limited boot media.

Clean up old logs/core dumps on the boot media; monitor free space and set an alert threshold (e.g., > 80% device usage).

If USB/SD is the only boot device option, use high-quality media and treat boot device as critical infrastructure—monitor it regularly.

Scenario 52: Mis-Configured VMkernel Ports for Storage / vMotion Causing Migration & I/O Failures

A vSphere cluster experienced intermittent vMotion failures and increased storage I/O latency during uplink failovers. On deeper inspection, the VMkernel adapters carrying storage and vMotion traffic were sharing uplinks or lacked redundant links, causing traffic loss when a physical NIC or uplink failed.

Symptoms:

vMotion tasks fail or hang mid-flight with errors such as “Host not accessible for migration”.

Storage latency spikes on one host correlating with uplink failover or link drop events.

Host logs show VMkernel link down/up events tied to VMkernel adapters used for storage/vMotion.

Root cause analysis:

vSphere best practice advocates separating traffic types (management, vMotion, storage, vSAN) with distinct VMkernel adapters and uplink groups. When these are overlapped (e.g., storage and vMotion sharing the same uplink), a failure in the uplink or NIC impacts multiple services simultaneously. Network mis-configuration is frequently cited among top VMware issues.

Troubleshooting steps:

On each host: Networking → VMkernel Adapters; check each adapter’s “Enabled services” (e.g., vMotion, vSAN, Provisioning).

Check the uplink/teaming assignment: ensure that uplinks assigned to the VMkernel adapters are distinct and provide redundancy (active/standby).

Review host logs (/var/log/vmkernel.log) for “vmk link down” events corresponding to storage/vMotion failures.

If possible, simulate uplink failover during off-peak to see how storage/vMotion behave.

Solution:

Create/dedicate separate VMkernel ports for storage and vMotion traffic, each with its dedicated uplink group or NICs.

Configure teaming/failover correctly—with redundant physical NICs/paths and ensure each traffic type has independent failover capability.

Monitor uplink status, VMkernel adapter status, and failover events; alert when a critical traffic adapter’s uplink fails.

Scenario 53: Licensing Edition Drift Leading to Feature Loss & Audit Risk

In an organisation that expanded its virtual environment over time, new hosts and clusters were added with mismatched licensing editions. After an upgrade, features like vMotion or DRS stopped working on some hosts, and an internal audit flagged unsupported features being used due to licence-edition mismatch.

Symptoms:

Some hosts show missing features (e.g., vMotion) though previously available.

vCenter → Licensing shows licence edition doesn’t support the features currently enabled.

Audit identifies usage of advanced features on hosts licensed for lower edition.

Root cause analysis:

License management often gets neglected in virtual environments. When features are assumed permitted (but host edition doesn’t support them) upgrades or audits can cause surprises—functional loss or compliance issues. Edition/drift mismatches are widely reported in VMware-admin challenges.

Troubleshooting steps:

In vCenter: Administration → Licensing → Licenses: list each host/cluster, its assigned license edition and expiry.

Review features used per host (e.g., Distributed Switches, vMotion, DRS) and map them to the licence editions required.

Identify hosts where feature-usage exceeds license entitlement.

Check change control logs: was a host cluster upgraded but license not updated accordingly?

Solution:

Align all hosts to correct license edition that supports their feature set. If mismatch, upgrade licence or remove unsupported features.

Implement quarterly licence audits and inventory tracking of edition vs feature usage.

Integrate licence review into change-control/upgrade process: any host addition or feature enablement must validate licence first.

Scenario 54: Nested Virtualization Left Enabled in Production Leading to Security Exposure

A lab/test cluster had nested virtualization enabled (vhv.enable = TRUE) for test VMs. Later, some production VMs were migrated to that cluster inadvertently and the nested-capability remained active. A security review discovered that this configuration exposed the hypervisor layer via guest VMs, increasing risk of “VM escape” or other hypervisor-based attacks.

Symptoms:

VMs with “Expose virtualization to guest OS” setting enabled in a production cluster.

Security audit flags nested virtualization enabled on prod hosts.

Unexpected VM behaviour or elevated privileges inside guest OS showing virtualization-capable features.

Root cause analysis:

Nested virtualization is typically intended for lab/test—not production. Leaving it enabled in production increases the attack surface (virtual machine escape, hyperjacking concepts) and indicates configuration drift. Virtualization security advisories warn of such exposure.

Troubleshooting steps:

Inventory all VMs: check setting Expose virtualization to guest OS or vhv.enable = TRUE.

Identify production clusters/hosts where nested virtualization should not be permitted.

Perform a security audit: look for unexpected access, elevated privileges, hypervisor-capability inside guests.

Check change records: was nested enabled for test then mistakenly left in production?

Solution:

Disable nested virtualization (vhv.enable = FALSE) for production VMs unless strictly required.

Create a baseline/hardening policy that forbids nested virtualization in prod clusters.

Schedule periodic audits of VM advanced settings; alert on nested virtualization enabled in production.

Scenario 55: Ghost / Orphan Snapshots Filling Datastore & Causing Storage Latency

Admins observed that one datastore’s free space was continually decreasing despite no large workload additions. At the same time, VM performance on that datastore degraded due to increasing storage I/O latency. Investigation found a number of hidden -delta.vmdk snapshot files even though VMs showed no snapshots in Snapshot Manager. These orphaned snapshots were consuming space and contributing to I/O backlog.

Symptoms:

Datastore free space dropping unexpectedly.

Some VMs show “Needs Consolidation” though no snapshots visible.

Storage latency (IOPS queue, latency) increases for VMs on the datastore.

Root cause analysis:

Snapshots when not properly managed or consolidated leave delta files that still consume space and add overhead to I/O. Over time, this hidden overhead causes performance and capacity problems. Snapshot age and size are widely cited among common VMware issues.

Troubleshooting steps:

On datastore, list large files matching *-delta.vmdk, *-redo.vmdk that don’t correspond to visible snapshots.

In vCenter: check VMs with Snapshot Manager for “Needs Consolidation”.

Monitor datastore space usage and performance metrics (queue depth, latency) for the relevant datastore.

Review host logs for warnings about snapshot chains or consolidation issues.

Solution:

For impacted VMs: consolidate snapshots (right-click VM → Snapshots → Consolidate) even if none are visible.

Establish snapshot governance: define retention period (e.g., no snapshots older than 48 h), size limits, and automatic cleanup.

Monitor for orphan snapshot chains and set alerts for *-delta.vmdk file size growth.

Educate teams: snapshots are not substitutes for backups and should not remain indefinitely.