VMware Realtime Interview Questions

Part I

Scenario 1: VM or Host Freezing Randomly

Symptoms

One or more virtual machines (VMs) become unresponsive (“frozen”) at random intervals.

The underlying ESXi host may also appear to “hang” or become non-responsive in the vCenter.

No obvious surge in CPU/memory usage just prior to freeze.

Possibly associated with large number of snapshots present.

Likely Root Cause

Accumulation of VM snapshots leads to large delta files, growing over time and impacting VM or host I/O or datastore performance. (One user noted: “VMWare apparently checks against all previous snapshots, and the freezing can happen if the delta becomes too large.”)

Possibly underlying host hardware issue, or memory module fault, but the strong correlation with snapshots suggests storage/delta growth issue.

Snapshot > datastore space full, or many chained snapshots causing heavy I/O, causing VM or host freeze.

Troubleshooting Steps

Check datastore free space: is the datastore nearly full or gap between usage and free space very low?

Review snapshots for the VM(s) that froze: use vSphere Web Client → VM → Snapshots. Are there many snapshots, old snapshots, large size deltas?

On the ESXi host, review vmkernel logs (/var/log/vmkernel.log) for I/O latency, storage stuck operations.

Check host health: memory error counters, CPU machine check events, hardware sensors (though if snapshots are the issue, hardware may be fine).

Attempt to consolidate snapshots: in VM’s Snapshot Manager choose “Consolidate” if it shows a “needs consolidation” warning.

After consolidation, observe whether freeze events cease or reduce in frequency.

Solution

Delete or consolidate unnecessary snapshots. Best practice: avoid long‐lived snapshots; keep them short–term (<1 week) and small size.

Free up datastore space to ensure there’s at least 20-30% free space (or as per vendor recommendation) for VM and snapshot operations.

Review snapshot policy: implement governance so snapshots are removed quickly after use (e.g., after backups).

If host continues to freeze after snapshot cleanup, consider hardware diagnostics (memory, storage controller) and review kernel logs.

Blog‐Post Takeaways

Emphasize the risk of “innocent” snapshots that linger.

Provide a step-by-step “snapshot clean-up” checklist.

Highlight how I/O latency effects from snapshots propagate to “freeze” symptoms.

Suggest monitoring: alert on > X days snapshot age or > Y GB snapshot size.

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Scenario 2: VM Performance Degradation — High CPU Ready Time

Symptoms

A VM reports high CPU usage, but inside the guest OS processes don’t fully account for the load.

The vSphere performance charts show high “CPU Ready” time (the time a vCPU is ready but waiting for physical CPU scheduling).

Applications inside the VM having latency or slow response even though host appears not saturated.

Likely Root Cause

Oversubscription of vCPUs on the ESXi host: too many vCPUs assigned relative to physical CPU capacity.

Resource contention: the VM is queued waiting for physical CPU cycles.

Possibly misconfigured reservations/limits or affinity settings causing skew.

Troubleshooting Steps

On the host, check summary performance: is CPU % busy very high (e.g., > 80-90%)?

On the VM in vSphere Web Client → Performance tab → Advanced → CPU → Ready Time (in ms). A rule of thumb: if average ready > 10-20 ms (or > 5% of CPU time) you may have contention.

Guest OS: check processes consuming CPU. Is there an anomaly? Could be guest‐side issue but if CPU ready is high, scheduling delay is likely.

Check vCPU count: how many vCPUs are assigned versus host physical cores/sockets.

Check other VMs on the same host: are they also impacted? Is the host “crowded”?

Review reservations/limits: if limit is set too low, or reservation too high causing others to starve.

Solution

Reduce number of vCPUs on the VM to what is actually needed (right‐size). Fewer vCPUs can reduce scheduling overhead.

Move the VM to a less loaded host (via vMotion) if host is oversubscribed.

Reconfigure resource pools/reservations to ensure fair allocation and avoid CPU starvation.

Consider scaling out rather than up (e.g., more VMs with fewer vCPUs) if workload allows.

Monitor CPU Ready over time after changes to confirm improvement.

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Scenario 3: Networking Issues – vMotion Fails at 14% with “Hosts not able to connect over vMotion network”

Symptoms

A vMotion operation fails part‐way through (e.g., at ~14 %) with an error similar to: “The vMotion migrations failed because the ESX hosts were not able to connect over the vMotion network.”

After failure, VM remains on original host; vCenter logs show network connectivity error or mismatched vMotion configuration.

Likely Root Cause

Misconfigured vMotion network: wrong subnet, mismatched MTU, missing NIC path or disabled vMotion service on one host.

Shared storage or host connectivity issue (though the error emphasises vMotion network).

Possibly firewall/port blocking between hosts on the vMotion network.

Troubleshooting Steps

On both source and destination hosts: check that vMotion VMkernel port is configured, enabled, and active.

Verify that the vMotion network is on the same subnet and reachable (ping/traceroute between the VMkernel vMotion IPs).

Check MTU settings if using jumbo frames: both hosts must agree (e.g., 9000); mismatch can cause failure.

On hosts: check “Networking → VMkernel adapters” and ensure “vMotion” checkbox is selected (for older vSphere versions).

Check firewall settings or intermediate switches: are vMotion ports allowed/forwarded?

Review vCenter and host logs for vMotion errors (look for vmkernel/vmotion messages).

Attempt a simpler VM or smaller workload to isolate if specific VM is the issue.

Solution

Correct the vMotion network configuration: ensure matching subnet, correct VMkernel adapter, correct service enabled.

Align MTU on both hosts and the network path if jumbo frames are used.

Ensure proper NIC teaming and dedicated vMotion network as best practice (reducing congestion).

If performing cross‐site vMotion, ensure network latency is within supported limits, and replication/storage configuration is correct.

Retry vMotion after fixes; monitor logs to confirm success and no residual errors.

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Scenario 4: Snapshot Age & Size Causing Performance / Stability Trouble

Performance of VM gradually degrades over time (higher latency, slower I/O).

vCenter shows “Consolidation needed” for VM.

Datastore full error or host showing storage latency spikes.

Likely Root Cause

Persistent large or chained snapshots accumulate; delta files become big and impact I/O operations.

Snapshots create overhead: every I/O may traverse parent + snapshot chain, causing latency.

Datastore space issue: snapshots remain on same datastore as VM, consuming capacity and causing other VMs to suffer.

Troubleshooting Steps

In vCenter, locate VMs with snapshots: use VM Summary → Snapshots, or via script (PowerCLI) to list age/size.

Check for “Needs Consolidation” status in vSphere.

On datastore: review free space, identify snapshot file sizes (look for *-delta.vmdk files).

Review VM kernel logs / host logs for storage latency warnings.

If VM is impacted: schedule snapshot consolidation or full deletion outside business hours.

Solution

Consolidate or delete snapshots: use Snapshot Manager or PowerCLI; ensure backup exists before deletion.

Implement policies: snapshots should be short-lived (e.g., <24-48 hrs) and < X GB (e.g., 5-10 GB) in size.

DNSstuff

Monitor snapshot age/size periodically and alert if exceeding thresholds.

Educate administrators/users that snapshots are not backups.

If datastore is near capacity, free up space (move VMs off, remove old files) to prevent cascade failures.

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Scenario 5: Storage Performance Degradation due to I/O “Blender”

In one datacenter running a VMware vSphere cluster, administrators began noticing that certain VMs — particularly those with heavy I/O (database, log-intensive) — were showing degraded performance: slower response, long IO wait times, and occasional alerts of storage latency. The host metrics didn’t point to CPU or memory saturation — instead, storage latency and queuing were the clear outliers.

Symptoms:

VMs experiencing sluggish performance.

Storage latency (device or datastore) elevated.

Hosts show normal CPU/memory usage, but storage subsystem reports high latency or I/O queue depth.

Possibly alerts in the host or storage array about queuing or slow responses.

Root cause analysis:

One of the articles summarises the issue: in virtual environments, multiple VMs on multiple hosts produce an “I/O blender” effect — many random I/O requests— which can degrade storage performance if the underlying storage isn’t designed for it.

Also, mis-configured storage paths, path selection policy (PSP), old firmware/driver versions, or lack of enough free space on datastores can worsen the situation.

Troubleshooting steps:

Monitor storage latency on hosts and VMs: check datastore latency, device latency, queuing.

Check free space on datastores: low free space can cause concatenated slow-downs.

Verify storage array health: any hardware alerts (controllers, disks), outdated firmware or drivers.

Check path selection policy (PSP) and multipathing configuration: ensure paths are active, consistent, no hanging paths.

Look at VM distribution: Are many heavy I/O VMs on the same host or datastore, causing hot-spots?

If using thin provisioned storage or shared resources, check for underlying contention.

After making changes (freeing space, balancing VMs, updating firmware), re-measure latency.

Solution:

Free up space on datastores so that there is healthy headroom (e.g., > 20-30 % free) for snapshots, I/O metadata, and guest activity.

Update storage array firmware + driver versions on hosts to ensure compatibility and performance.

Ensure multipathing is properly configured: correct PSP, no dead paths, consistent across hosts.

Balance heavy I/O VMs across hosts and datastores to avoid bottlenecks.

If underlying storage is insufficient for workload, consider migrating to higher performance tier (e.g., all-flash array, faster controllers) or redesigning for higher IOPS.

Monitor going forward: set alerts on latency thresholds, queue depth, datastore free space.

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Scenario 6: Mis-configured Resource Pools Causing “Noisy Neighbor” VM Impact

In a medium-sized VMware environment, several critical VMs began showing intermittent performance problems: slower response, inconsistent latency. On investigation, the root cause wasn’t storage or network, but resource contention inside the same host: one VM was hogging resources and starving the others. The team found that resource pools had been created years ago, but the configuration hadn’t been revisited as workloads changed.

Symptoms

VMs on the same host show erratic performance (some good, some poor).

Host CPU/memory usage may appear moderate, but particular VMs have high CPU Ready times or memory ballooning.

The “noisy neighbor” effect: one VM dominating the host.

Root cause analysis

Resource pools allow grouping of VMs with resource shares, limits, and reservations. But if configured poorly (e.g., unlimited limits, too many shares, or mis-set reservations), one VM or pool can starve others. Also, as workloads evolve, initial allocations become outdated. A monitoring guide mentions that “storage is typically the source of most performance problems… but CPU/memory resource contention remains very relevant.”

Troubleshooting steps

Identify which VMs are showing symptoms; look at their Host/VM summaries in vCenter (CPU Ready, memory ballooning, latency).

Check resource pool configuration: what are the shares, limits, reservations? Are there any unusual limits set?

On the ESXi host, check overall load vs what resources are allocated to the problem VMs.

Check for recently grown or changed VMs (maybe someone upgraded vCPUs or memory) that may now impose heavier load.

Consider vMotion migrating some VMs off the host to relieve load and isolate whether it is indeed resource contention.

Solution

Right-size big VMs (reduce vCPUs/memory to what they actually need).

Update resource pools: set meaningful reservations/limits/shares based on business priority.

Use DRS (Distributed Resource Scheduler) or host balancing to distribute workloads evenly.

Monitor CPU Ready, memory ballooning metric continuously; set alerts for anomalies.

Document resource pool strategy — ensure future VM deployments adhere to it.

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Scenario 7: DR/Replication Failure — VM Replication Stops Without Warning

An organization used VMware Site Recovery or replication between two sites for disaster recovery. During a planned failover test, many VMs were missing or out-of-sync. On closer look, replication had silently stopped days earlier due to a change in storage path and was not detected until the test.

Symptoms

Replication health status shows “OK” but data is out-of-date.

On failover, missing VMs or data loss.

Storage or network path changes had been made recently which disabled replication silently.

Root cause analysis

Replication frameworks (whether native vSphere Replication or third-party) depend on constant storage path, network connectivity, and correct configuration. When someone changes a storage LUN mapping, network path, or firewall rule, replication can stop or error out silently. Monitoring may still show “connected” even though replication isn’t actually writing data.

Troubleshooting steps

Check replication logs: last successful cycle timestamp vs current time.

Verify storage path and network connectivity between sites for replication traffic.

Review recent changes: storage reconfig, LUN re-mapping, network change.

Validate replication policy compliance: RPO (Recovery Point Objective), replication schedule.

On failover site, check for missing or stale snapshots/replicas.

Solution

Implement proactive monitoring/alerts specifically on replication lag, failed cycles, stale data.

Ensure changes to storage or network are reviewed for impact on DR/replication workflows.

Test failover regularly (e.g., semi-annually) to validate that replication works end-to-end.

Document replication architecture and dependencies; classify critical VMs and ensure they have high RPO/RTO replication.

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Scenario 8: Security Mis-configuration — vSphere Integrated with Active Directory Creates Attack Surface

A large enterprise had deeply integrated vSphere infrastructure (ESXi hosts, vCenter) with their central Microsoft Active Directory (AD) for single-sign-on and ease of management. However, after an AD credential compromise, attackers used that to gain privileged access to vCenter and ESXi, leading to wide virtualization traffic takeover.

Symptoms

Unusual login events in vCenter tied to AD accounts.

ESXi hosts suddenly re-configured, VMs moved/modified.

Audit logs show lateral movement from AD to virtualization infrastructure.

The cloud blog from Google/Mandiant highlighted such risks: “This direct link can turn an AD compromise into a high value scenario for the entire vSphere deployment.”

Google Cloud

Root cause analysis

While AD integration simplifies identity management, it also creates a single high-impact path: if AD credentials are compromised, attackers can pivot to VMware infrastructure. Often default trust, broad privileges, and lack of micro-segmentation magnify the issue.

Troubleshooting steps

Review audit logs in vCenter and ESXi for unusual auth events or privilege escalations.

Identify which AD accounts are trusted for vCenter or ESXi and what permissions they have.

Validate that hosts are still compliant with security baseline: NTP sync, certificate validity, unnecessary services disabled. Best practice blog highlights: disable SSH unless needed, ensure NTP configured, etc.

Medium

Assess network segregation: is virtualization management traffic separated from general user networks?

Solution

Restrict AD accounts allowed to access vCenter/ESXi; enforce least-privilege.

Use dedicated admin domain or separate AD OU for virtualization management.

Separate management network physically or logically from production networks.

Enable multi-factor authentication (MFA) for vCenter/ESXi logins.

Regularly review and audit roles/permissions; remove unused accounts.

Harden hosts: disable unnecessary services, ensure time-sync, regularly update certificates and keys.

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Scenario 9: vMotion Upgrade Issue — Cluster Upgrade Blocked by Unsupported Host Version

While upgrading the vSphere cluster to version 9.0, the team discovered that some hosts still ran version 7.x and could not be managed by the new vCenter version. This blocked migrations and upgrades until all hosts were aligned. The “What’s New” blog by VMware notes: vSphere 9.0 “supports direct upgrade from vSphere 8.0. Upgrading directly from vSphere 7.0 is not supported.”

VMware Blogs

Symptoms

Upgrade wizard fails or issues a warning: host version not supported.

Hosts show as non-compliant in vCenter Lifecycle Manager.

vMotion tasks or DRS migrations fail or are prevented.

Root cause analysis

Major version upgrades often come with compatibility constraints. For example, vCenter 9.0 cannot manage ESXi 7.0 hosts. If hosts are out of date, you cannot proceed. The teams sometimes skip interim upgrades assuming direct jump is possible, which leads to these blocks.

Troubleshooting steps

Check the current versions of all ESXi hosts and vCenter.

Validate upgrade path: is direct upgrade supported from current version to target?

Identify hosts with old hardware or unsupported versions causing blockage.

Review Lifecycle Manager compliance status: image-based vs baseline remediations.

Solution

Plan upgrade path early: if hosts are on v7.x, first upgrade them to v8.x (or supported intermediate) before going to v9.0.

Use image-based lifecycle management as required by new versions (as per VMware documentation).

Retire or replace hosts that cannot be upgraded (unsupported hardware or vendor limitations).

Perform upgrades in phases; validate after each step; maintain backup/rollback plan.

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Scenario 10: Storage Snapshot Sprawl in vSAN and Datastore Causing Latency and Capacity Issues.

In a vSAN environment, administrators noticed increasing storage latency and declining free space. Investigation revealed many long-lived snapshots (some weeks old) and chained delta files accumulating. The official vSAN failure scenarios blog explains how “absent” vs “degraded” states cause rebuilds and how space and timers matter.

Symptoms

Datastore free space diminishing fast.

Storage latency rising for VMs (I/O wait, slow application response).

vCenter shows “Needs Consolidation” for multiple VMs.

vSAN health alerts: objects absent or non-compliant, rebuilds queued.

Root cause analysis

Snapshots are not meant to be long term. In vSAN, when a component fails or is absent, there is a rebuild timer delay (default 60 minutes) to avoid unnecessary rebuilds for transient issues. However, with many snapshot chains and low spare capacity, this can compound performance problems. The “I/O blender” effect in virtual environments makes matters worse.

Troubleshooting steps

Identify VMs with snapshots: list age, size of delta files.

Check datastore/vSAN free capacity and health: “Physical disks” and “Disk groups” in vSAN health.

Monitor storage latency and IOPS on hosts/datastores.

Investigate snapshot management policy: are snapshots being kept too long? Are they part of backups?

In vSAN: verify rebuild timer delay, object states (absent/degraded).

Solution

Clean up unwanted snapshots immediately; consolidate or delete older than a set threshold.

Implement snapshot governance policy (e.g., snapshots older than 48 h or >10 GB auto-flag).

Ensure adequate spare capacity in vSAN disk groups so rebuilds don’t degrade performance.

Adjust rebuild timers if your SLA demands faster rebuild (but do so understanding the impact).

Monitor storage metrics ongoing; set alerts for latency >10 ms or free space drop below threshold.

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Scenario 11: Cluster Upgrade Gone Wrong — Deprecated APIs & Add-on Failures

During a planned major upgrade of a vSphere cluster (control plane + hosts + add-ons), the team upgraded the cluster to the supported version. Post-upgrade, some critical add-ons (ingress controllers, CSI drivers, network service mesh) failed to function correctly. Applications began experiencing failures or degraded behavior. On investigation, they discovered that several add-ons used deprecated Kubernetes or vSphere APIs that were removed in the target version, and snapshot/backup integration broke.

Symptoms:

Components such as storage CSI driver log errors about unsupported API versions.

New VMs or migrated VMs unable to use certain features (e.g., vMotion, snapshots) as before.

Services dependent on add-ons fail or applications misbehave.

Cluster hosts show “deprecated API usage” warnings.

Root cause analysis:

Whenever a vSphere upgrade is performed, the underlying Kubernetes version (for VCF or SDDC) or APIs for add-ons may change or be deprecated. If you don’t check compatibility of workloads, CRDs, drivers, and add-on components before upgrade, you risk functional regressions. Also, snapshots and backup workflows may rely on older APIs and break. The upgrade path may skip versions or remove features. Best practice documents emphasise checking deprecated APIs and compatibility.

Troubleshooting steps:

Inventory all add-ons, drivers, CRDs, custom integrations with versions and check vendor compatibility with target version.

Review host/cluster logs for warnings about deprecated API usage or unsupported version of components.

Check each critical workload for functionality post-upgrade: snapshots, vMotion, backups, application start/stop.

If an add-on fails, attempt to roll back the version or upgrade the add-on to a compatible version; review vendor documentation.

Verify cluster health: host versions, VM compatibility levels, tools versions (e.g., VMware Tools), driver/firmware versions.

Solution:

Before upgrade: build a “pre-upgrade compatibility matrix” of all add-ons, CRDs, drivers, and validate with vendors.

Ensure snapshots/data backup prior to upgrade; have rollback plan in case of issues.

Perform upgrade in a test/staging cluster first, simulating production workloads and add-on dependencies.

Post-upgrade: validate hosts, VMs, add-ons; address failures or regressions promptly (either by rolling back or updating add-ons).

Update documentation and runbooks to reflect new version dependencies and upgrade procedures.

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Scenario 11: Memory Over-commit & Ballooning Causing VM Slowdown

In a virtualization cluster, a team upgraded the consolidation ratio (more VMs per host) to save cost. After the change, several VMs began showing unexplained performance degradation — high guest OS memory usage, inside the VM high paging/ swap, and from the hypervisor side memory ballooning. They hadn’t accounted for memory resource management properly.

Symptoms

Guest OS page file usage is high though host has “free” memory reported.

In vSphere performance charts: “Balloon” activity spikes; memory swap used.

The host memory appears busy; VM response times increase.

Root cause analysis

Memory over-commitment in virtual environments allows you to assign more combined guest memory than physical host RAM. Techniques like ballooning and swapping allow the hypervisor to reclaim memory. But if too aggressive, it can lead to performance issues. A study of memory ballooning techniques shows the overhead and risks of these mechanisms.

Also a monitoring article points out that monitoring memory ballooning and swap usage is critical.

Troubleshooting steps

In vSphere, check memory metrics per host: “ballooned memory”, “swapped memory”, “consumed memory”.

For the affected VMs, check guest OS memory paging or swap usage.

Review host total memory assigned vs physical and check how many VMs have large memory allocations.

Identify whether resource pools/reservations/limits are mis-configured such that some VMs hog memory.

Consider reducing memory allocations or migrating some VMs off the host.

Solution

Right-size guest memory allocations: allocate only what is needed and monitor afterward.

Avoid over-commitment beyond what workload and performance metrics support.

Configure resource pools with proper shares/limits/reservations if needed.

Monitor ballooning and swap; set alerts for ballooned memory > X% of host.

If persistent high memory pressure, consider host hardware upgrade (more RAM) or migrate workloads.

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Scenario 12: Network Latency in vSphere Affects vMotion & Storage Traffic

A company using vSphere with shared storage and a vMotion network across hosts started seeing frequent vMotion failures and storage I/O bottlenecks. The network fabric hadn’t been upgraded in years and was beginning to show packet drops, latency spikes, layering issues (storage+vMotion+management traffic on same network).

Symptoms

vMotion tasks fail or hang (or take far longer than usual).

Storage latency rises in certain hours, especially when migrations or backups happen.

Network monitoring shows packet loss or high latency on transport relevant to hosts.

Root cause analysis

In virtualised infrastructure, while CPU/memory contention are easier to spot, network (especially for vMotion, storage or vSAN traffic) is often the hidden bottleneck. The monitoring guide says: “Network bottlenecks in vSphere are typically less common, but packet drops… virtual or physical switch level… high latency between VMs… may cause application performance problems.”

Consolidating different traffic types (storage, vMotion, management) on the same network path without proper segregation, teaming, or MTU configuration can degrade performance significantly.

Troubleshooting steps

Monitor network metrics: packet drops, latency, throughput on hosts and switches.

Verify physical switch uplinks, VLAN segmentation, NIC teaming, utilization on each link.

Ensure that vMotion/Storage traffic is separated from standard VM traffic (or at least properly prioritized).

If using jumbo frames for storage/vMotion, verify MTU consistency across hosts and switches.

Test migration/storage activity during off-peak to isolate network impact.

Solution

Segment traffic: Create separate physical/logical networks for vMotion/storage/management.

Upgrade network hardware if it is outdated or overloaded (higher bandwidth or dedicated links).

Configure proper NIC teaming/failover and verify switch configurations (spanning tree, port speed).

Ensure MTU/jumbo frame settings are consistent.

Monitor regularly: track network latency and set alerts for packet loss or link saturation.

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Scenario 13: Cluster Service (vCLS) Mis-configuration Causes DRS/HA to Stop Working

After an upgrade to VMware vSphere 7.0 Update 1, a cluster started behaving oddly: automatic DRS migrations stopped, and HA behavior during host failures became manual. The root cause turned out to be missing or mis-configured vSphere Cluster Services (vCLS) agent VMs. A VMware blog explains the architecture and health considerations of vCLS.

Symptoms

DRS shows disabled or not functioning.

On host failure, HA still restarts VMs but placement isn't optimal; DRS will not rebalance.

Cluster summary alerts: “vSphere Cluster Services agents missing/unhealthy.”

Root cause analysis

In vSphere 7.0 U1 and onwards, vCLS enables cluster services (DRS/HA) to run independently of the vCenter Server availability. The cluster deploys 1–3 small agent VMs (depending on host count) to maintain cluster service quorum. If those agent VMs are absent (e.g., due to datastore constraints or misconfig), those core services may degrade.

Troubleshooting steps

Inspect the VMs & Templates view for vCLS agent VMs (they are thin provisioned, minimal size) on the cluster.

Check Cluster > Configure > vSphere Cluster Services health for “Healthy / Degraded / Unhealthy”.

Confirm that the shared datastore exists and hosts have access (agent VMs need shared storage).

Review host logs for errors about vCLS agent VM deployment or power-on failure.

Solution

Ensure each host can host the vCLS agent VMs (adequate resource, datastore visibility).

If vCLS is degraded, migrate VMs off host causing issue and reboot host or fix storage path.

Avoid placing vCLS agents on local-only datastores where possible; use shared storage.

Post-fix, verify DRS/HA resumes fully and agent VMs are present across hosts.

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Scenario 14: Security Breach via vSphere – Trojan Path to Hypervisor

A security team discovered that attackers gained access not via obvious servers, but via the management plane of the hypervisor infrastructure (management network of vCenter/ESXi). The attackers had compromised an AD account and used it to access vSphere, then deployed malicious VMs and moved laterally. A blog by the Google Threat Intelligence Group discusses how threat-actors target vSphere environments: “Their strategy is rooted in a living-off-the-land approach… after social engineering one account they pivot to vSphere.”

Symptoms

Unusual login events in vCenter or ESXi hosts, especially from unexpected IPs.

Creation of unknown VMs or snapshots, changes to host configurations, unusual power-ons.

Lack of regular logs or unexpected stretching of privileges.

Root cause analysis

Hypervisor infrastructure is highly trusted and powerful; if attackers gain access they gain broad control. Integration of vSphere with centralized identity systems (e.g., Active Directory) increases risk if credentials are compromised. The blog notes that logs often aren’t forwarded or audited properly, making detection hard.

Troubleshooting steps

Review vCenter & ESXi logs: user login events, VM creation, host config changes.

Ensure that audit logs are forwarded to a central SIEM and retention is set.

Review all privileged accounts: are there stale accounts, service accounts abused?

Check network segmentation: management networks should be isolated from user networks.

Verify that hosts and vCenter are patched, hardened (disabling SSH unless needed etc.).

Solution

Implement least-privilege access: only authorized accounts should access vSphere management.

Enable MFA for vCenter/ESXi management access.

Ensure management networks are isolated and firewall-protected.

Forward all logs to SIEM; set alerts on critical events (unauthorized VM creation, host config changes).

Periodically review security posture: audit accounts, certificates, wipe unused accounts.

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Scenario 15: DR Test Reveals Storage Compatibility Issue — Failover Fails Under Load

The story

During an annual disaster recovery test, an organization attempted to failover VMs to its DR site (replication target). However, as VMs powered on, storage controllers at DR site began saturating, performance collapsed, and some VMs failed to start. After investigation, they discovered the DR site storage array used older firmware/drivers incompatible with large replication loads in the target environment.

Symptoms

Failover test: VMs power-on but respond slowly or time-out.

Storage latency at DR site spikes to high values; VM guest OS shows I/O timeouts.

Replication logs show write backlog or target site errors.

Root cause analysis

Disaster recovery is more than just replication — the target site must be designed to absorb full production load during failover. If storage hardware/fabric at DR site is under-provisioned or uses older unsupported firmware/drivers, it might get overwhelmed. Problems are often masked until failover. Monitoring articles on vSphere performance emphasise that storage is typically the source of most performance problems.

Troubleshooting steps

Review replication logs: measure lag, backlog, error rates.

At DR site, monitor storage subsystem during failover: IOPS, latency, queue depth.

Check storage array firmware/driver versions; compare with vendor compatibility lists.

Simulate partial failover test ahead of schedule to reveal capacity bottlenecks.

Solution

Ensure DR site has storage hardware and firmware/drivers that can support full production workload.

Regularly test failover — not just baseline but load-test to failure to discover weak points.

Maintain inventory of hardware/firmware and update to supported versions.

Document failover plan and trigger list; ensure team understands performance expectations.

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Scenario 16: Storage Tiering Mis-Configuration Causing Unexpected Latency

The story

An enterprise decided to implement automated storage tiering within their VMware vSAN (ESXi) cluster in order to move less-used data to slower tiers and keep hot data on NVMe flash. Initially promising, after a few weeks some business-critical VMs began showing sporadic high latency. On investigation, the tiering policy had been mis-applied, and some hot data had already migrated to slower tiers, plus the tiering engine was overwhelming the storage fabric.

Symptoms

VMs display occasional I/O latency spikes though host CPU/memory look moderate.

Storage latency graphs show spikes divergent from expected pattern (e.g., during tiering operations).

Datastore tiers show heavy activity on “cooler” tier drives and flash tier utilization not as expected.

Alerts or logs indicating slow response times on some disks or datastore objects.

Root cause analysis

Tiering systems rely on accurate data usage patterns and correct policy definitions. If the policy is too aggressive (e.g., moves data too frequently), or if hardware isn’t sized properly for the tiering workload, performance will degrade. In addition, some experimental features like NVMe memory tiering (using SSD/NVMe as an extension of RAM or cache) are still emerging and have known limitations. For example, one community discussion suggests:

“Write that then… I don’t think my expectations are unreasonable… It became unusable after an ESX patch.”

Reddit

Troubleshooting steps

Monitor storage IOPS, queue depth and latency across tiers (flash vs spinning disk) and identify which VMs are impacted.

Check the tiering policy settings: which drives are designated for hot data, how often movement occurs, thresholds defined.

Check underlying hardware: are the tier drives (e.g., NVMe/SSD) performing as expected, or showing increased latency themselves?

Review whether the tiering process is competing with production workload (e.g., background movement tasks).

If using memory‐tiering (NVMe as memory extension) check compatibility/limitations (some migrations or snapshots may fail).

Solution

Re‐evaluate tiering policy: tighten threshold definitions, reduce movement frequency, ensure only truly “cool” data is moved.

Ensure that hardware tiers are sized properly: flash/NVMe must be able to handle hot workloads; slower tiers must not host active production VMs by mistake.

If using experimental tiering or memory‐tiering features, validate in test environment first and be aware of features not supported (e.g., certain snapshot types).

Monitor after change: expected latency reductions, improved VM responsiveness, correct tier usage patterns.

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Scenario 17: VM Tools / Virtual Hardware Version Mismatch Leads to Guest Instability

The story

During a mass hardware refresh and ESXi upgrade, an operations team upgraded host versions and then proceeded to upgrade guest VM hardware versions (virtual hardware compatibility) and guest tools (VMware Tools). Shortly thereafter, several Linux and Windows VMs experienced driver issues, network drop-outs, or failed to reboot reliably.

Symptoms

VMs fail to power on, or after powering on show device missing errors.

Guest OS reports driver failures (network or graphics).

Backups or snapshots fail with errors referencing “unsupported hardware version”.

Hosts report that VM hardware version is newer than host supports. For example, an article states:

“A VMware product is unable to power on a VM if its hardware version is higher than this product supports.”

Root cause analysis

Virtual machines have a “hardware version” which dictates capabilities (e.g., number of vCPUs, maximum memory, device support). If you upgrade hardware version without verifying guest OS support or host compatibility, problems arise. VMware recommends upgrading tools before upgrading virtual hardware.

Support Portal

Also, the Tools version must be compatible with guest OS; failure to verify can cause driver issues.

Troubleshooting steps

Identify impacted VMs: check hardware version, VM Tools version, guest OS version.

Check host compatibility: whether host ESXi version supports that VM hardware version.

For each VM, check Tools status (good, outdated, none) and driver errors in guest OS.

Examine recent upgrade events: which VMs had hardware or tools upgrades before issues.

Attempt roll-back: revert to older hardware version (if snapshot/backup exists) or reinstall Tools.

Solution

Upgrade VM Tools first (while guest OS still supports) before changing hardware version.

Only upgrade hardware version when host and guest OS have been validated for compatibility.

For large environments, stage rollout: upgrade a small group, validate, then proceed.

Maintain inventory of VM hardware versions and Tools versions; set alerts for out‐of‐date Tools.

==================================================================================================================================

Scenario 18: Stretched vSAN Cluster Issues – Split-Brain and Rebuild Delays

The story

An organization deployed a stretched vSAN cluster across two sites for high availability and disaster recovery. During a network flap between the two sites, the cluster entered a ‘partitioned’ state. Some objects became “absent” and rebuilds did not start automatically due to default timer settings. VM performance degraded as rebuilds dragged on.

Symptoms

vSAN health shows ‘Degraded’ or ‘Absent’ components.

VM I/O latency increases or some VMs become unavailable.

Alerts about “vSAN object‐repair timer delay” or “component missing for > X minutes”.

Network logs show inter-site communication failure preceding the issue.

Root cause analysis

In a vSAN stretched cluster, communication between the two sites and the witness node is critical to maintain quorum and object availability. If connectivity fails, objects may become unavailable or rebuilds delayed. VMware’s default object repair timer (often 60 minutes) delays rebuild, which under load can degrade performance.

Poor network design (latency, scale) or insufficient witness placement can exacerbate.

Troubleshooting steps

Review vSAN health > physical disks/disk groups and object status in vSphere.

Check inter-site network connectivity: packet loss, latency, switch logs.

Review object repair timer settings and the counts of absent/degraded components.

Check if rebuild traffic is saturating network/storage and impacting production workloads.

Analyze how witness node is placed and if its connectivity remains stable.

Solution

Ensure network connectivity between sites is highly reliable and meets throughput/latency requirements for stretched vSAN.

Adjust object repair timer settings to match business SLA (e.g., shorten from 60 mins to 15–30 mins if necessary).

Monitor rebuild traffic and plan capacity so rebuilds do not starve production workloads.

Use vSAN witness and placement best practices to avoid single point of failure.

Schedule periodic failover/fail-back drills to test stretched cluster resilience.

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Scenario 19: Improper Backup Integration – VM Backups Failing After Storage Changes

The story

A mid-sized company uses a third-party backup solution integrated with their vSphere environment for VM backups and snapshot-based restore. After migrating VMs to a new datastore and changing storage paths, backups began failing silently. At the next restore test, several VMs could not be restored due to missing snapshot chains or incorrect metadata in backup vault.

Symptoms

Backup jobs show success, but restore test fails or VMs show data corruption/incomplete data.

Logs indicate “snapshot chain not found”, “vStorage API error”.

VMs that were moved or storage re-path changed are more impacted than others.

Root cause analysis

Backup solutions for vSphere often rely on consistent storage paths, snapshot chains, and vSphere APIs (e.g., vSphere Storage APIs – Data Protection, VADP). When storage is changed (datastore moved, renamed, re-mounted) without updating backup configuration, metadata mismatch leads to silent failures. A monitoring guide earlier noted: “storage is typically the source of most performance problems” but here it's also the source of functional backup problems.

Troubleshooting steps

Review backup solution logs for jobs targeting moved VMs or changed datastores.

Check snapshot chains for impacted VMs via vSphere Web Client – Snapshots tab.

Verify storage changes: which datastores were moved/renamed; whether backup jobs were updated accordingly.

Attempt manual restore for a known good VM to see if chain is intact.

Coordinate with storage team and backup vendor to ensure paths and metadata align.

Solution

Maintain a change control process: anytime storage/datastore changes occur, update backup configurations and test.

Monitor backup job health beyond “success” – include restore tests and validate chains.

Ensure backup solution is configured to detect moved/migrated VMs or datastore renames and flag jobs accordingly.

Regularly test restores (quarterly or semi annually) for critical VMs.

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Scenario 20: Patch-Management Failure – ESXi Hosts Remain Unpatched Leading to Vulnerability & Instability

The story

A health-care organisation running a VMware environment delayed ESXi and vCenter patches due to perceived risk of downtime. Over time, hosts began experiencing drive controller firmware inconsistencies, time-drift issues and even storage path interruptions. One incident revealed that a host was vulnerable to a known CVE and was exploited via a nested VM escape scenario.

Symptoms

Hosts show alerts for unsupported firmware or driver versions.

Time sync issues on VMs, guest clocks drifting.

Some VMs display hardware compatibility warnings.

Security scan surfaces known vulnerabilities in ESXi hosts.

Root cause analysis

Patch-management is critical to both performance and security in virtualization environments. Delaying ESXi, vCenter patches or firmware updates may lead to instability (drivers/firms mismatches) and security exposure. A blog noted that keeping hardware and drivers aligned is critical.

Troubleshooting steps

Use VMware’s Lifecycle Manager or other tool to audit host patch level, firmware/driver versions, BIOS versions.

Run vulnerability scan on hosts and check for outstanding patches/CVEs.

Review logs for storage path or NIC driver errors, time drift events.

Check host time sync with NTP and guest OS clocks for drift issues.

Solution

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

Use automation (Lifecycle Manager) for compliance and baseline remediation.

Implement test staging for patches before production rollout; ensure backups/snapshots exist before patch window.

Monitor host compliance; set alerts for non-compliance or known vulnerabilities.

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Scenario 21: Storage Tiering Mis-Configuration Causing Unexpected Latency

The story

An enterprise decided to implement automated storage tiering within their virtualised environment to reduce cost and optimise performance. They defined “hot” data to reside on fast SSD/NVMe and “cold” data to be migrated to slower HDD tiers. Initially the plan looked good — however several business-critical VMs began showing intermittent elevated I/O latency, slower application response, and inconsistent performance. On investigation it turned out that the tiering engine had mis-classified “hot” data as “cold” and migrated it to slower tiers, and moreover the tiering process itself was consuming storage bandwidth, affecting active workloads.

Symptoms

VMs experiencing sporadic high latency even though host CPU/memory were fine.

Storage performance charts show latency spikes corresponding with tiering movement operations.

Some datastores or tiers show unexpected load (slower drives/tiers handling “hot” data).

Administrators discover that tier-movement tasks (background) coincide with business workflow windows.

Root cause analysis

Automated tiering systems are powerful but can introduce problems in virtualised environments. They rely on correct policy definitions, correct detection of “hot” vs “cold” data, and underlying hardware that can sustain both productions and movement loads. If the tiering policy is too aggressive or mis-configured, data that should remain on the fast tier might get moved to a slower tier, increasing latency. Also, the background movement (re-placing data) may contend with production I/O. In virtual environments with many random I/O patterns (the so-called “I/O blender” effect), this mis-alignment becomes more acute.

Troubleshooting steps

Identify which VMs are impacted: correlate latency events with tiering/migration timelines.

Monitor storage IOPS, queue depth and latency per tier (fast vs slow) and for each VM.

Review tiering policy settings: what are the thresholds for “cold” data, how often is movement triggered?

Check hardware performance of tiers: Are SSD/NVMe drives performing to spec? Are slower HDD tiers overloaded?

Check when tiering movement tasks run. Are they scheduled in business hours? Are they impacting production workloads?

Solution

Adjust the tiering policy: make thresholds more conservative, reduce movement frequency, ensure only truly rarely-accessed data moves.

Ensure hardware tiers are correctly sized: fast tier must have capacity headroom; slower tier must not be used for active production data.

Schedule movement tasks in off-peak hours to reduce impact.

Monitor post-change: latency metrics should improve; ensure “hot” data remains on fast tier.

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Scenario 22: VM Tools / Virtual Hardware Version Mismatch Leads to Guest Instability

During a major host upgrade in their vSphere cluster, the operations team upgraded the ESXi hosts to a newer version and then proceeded to upgrade guest virtual machines’ hardware compatibility version (virtual hardware) and the VM Tools inside the guests. Very soon after, some Windows and Linux VMs started having driver errors, network connectivity failures, guest OS unable to boot or unstable behaviour.

Symptoms

VMs fail to power on or the guest OS shows device driver errors (network adapter missing, virtual NIC not recognised).

Backup snapshots fail with error referencing unsupported hardware version.

Hosts report VM hardware compatibility mismatch (VM version newer than host supports).

Root cause analysis

In VMware environments, each VM has a “virtual hardware version” (also called “VM hardware compatibility”) which dictates available virtual devices, vCPU/vMemory limits, etc. Upgrading this version before verifying host support or guest OS driver compatibility can cause major issues. Similarly, the VMware Tools package inside the guest must be compatible with both the guest OS and the host/hypervisor version. Upgrading tools/hardware too aggressively without validation can break stability.

Troubleshooting steps

Identify impacted VMs: list virtual hardware version and VM Tools version.

Check host compatibility: whether the ESXi host version supports that VM hardware version.

In guest OS, check device manager (Windows) or dmesg/lsmod (Linux) for missing drivers.

Roll back (if available) to previous hardware version or re-install VM Tools.

Solution

Upgrade VMware Tools first and confirm guest OS stability before changing virtual hardware version.

Only upgrade hardware version when host, guest OS and all drivers are validated.

Plan rolling upgrade: test a small subset of VMs, monitor, then roll out.

Maintain inventory of VM hardware versions and Tools versions; set alerts for “too new for host”.

========================================================================

Scenario 23: Stretched vSAN Cluster Issues – Split-Brain + Rebuild Delays

A customer deployed a stretched cluster using vSAN across two geographic sites for high-availability and disaster recovery. During a network event between the two sites, the cluster partially partitioned. Some vSAN object components became “Absent” or “Degraded”. Rebuilds did not start immediately (default timer delay) and performance degraded noticeably until rebuild completed. The misunderstanding around the repair timer, network dependency and capacity margin caused the issue.

Symptoms

vSAN health dashboard shows “Absent components” or “Degraded objects”.

VM I/O latency increases, some VMs become slow or unreachable during partition.

Logs show network disconnect between sites followed by rebuild backlog.

Root cause analysis

In stretched vSAN clusters, quorum/communication between sites and witness node is critical. When connectivity fails, clusters might enter split-brain scenarios or component rebuilds may delay due to default object repair timers. The rebuild process itself takes resources, and if hardware/tiering/space headroom is not sufficient, performance suffers. Also, mis-configuration (network latency too high, insufficient witness placement) heavy churn can worsen the condition.

Troubleshooting steps

Check vSAN health: object status, component counts, rebuild backlog.

Investigate network logs: inter-site latency, packet loss, uplink/downlink issues.

Inspect disk‐group spare capacity: are there sufficient spare resources for rebuild without impacting production?

Review object repair timer setting (e.g., 60 minutes by default) and how long components have been missing.

Solution

Ensure inter-site network reliability: low latency, high bandwidth, resilient links.

Adjust object repair timer based on SLA: shorten if your environment tolerates faster rebuilds.

Guarantee sufficient spare capacity in disk groups for fault tolerance and rebuilds.

Regularly test fail-over/fail-back scenarios to validate stretched cluster behaviour.

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Scenario 24: Improper Backup Integration – VM Backups Failing After Storage Changes

A mid-sized organisation used a third-party backup tool integrated with its virtualization environment (vSphere). After migrating VMs to a new datastore and performing storage path changes, backup jobs continued to report success. However, during restore testing, several VMs could not be recovered properly because the snapshot/metadata chain was broken. The storage change had invalidated the backup configuration and no one noticed until the test.

Symptoms

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

Error messages such as “snapshot chain not found”, “invalid vStorage API call”.

Storage migration logs showing VMs moved or datastores renamed without backup job update.

Root cause analysis

Backup integrations in VMware environments often rely on vSphere APIs (e.g., VADP), consistent datastore identifiers, snapshot chains, and metadata in the backup vault. Changing storage paths, migrating datastores, renaming storage without updating backup job configuration or metadata can cause silent failures: jobs run “successfully” but backup contents are invalid or restorations fail. This is a frequent overlooked issue in virtualised backup strategy.

Troubleshooting steps

Inspect backup job logs for VMs moved or datastores changed; check last successful backup date.

Verify snapshot chains for each VM: in vSphere, check Snapshot Manager and underlying VMDK delta files.

Check storage change activity: which VMs/datastores were moved, renamed, or remapped.

Attempt a test restore of an impacted VM to identify gaps in data.

Solution

Enforce change control: any storage/datastore change must trigger backup job review and validation.

Supplement backup job success with scheduled restore tests (not just “job ran”) to validate data integrity.

Ensure your backup tool has visibility of storage changes, and update configuration accordingly.

Monitor backups with additional metrics: last successful restore test, integrity check status, datastore/move change alerts.

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Scenario 25: Patch-Management Failure – ESXi Hosts Remain Unpatched Leading to Vulnerability & Instability

The story

A healthcare organisation delayed applying ESXi and vCenter patches citing “risk of downtime”. Over time, hosts began showing driver/firmware mismatches, time sync issues, and degraded storage path behaviour. Ultimately a known vulnerability in ESXi (exploited in the wild) led to host compromise, data encryption, and service outage.

Symptoms

Hosts report outdated firmware/driver versions in vCenter compliance view.

Time drift visible in VMs; guest OS clocks drifting; backup failures.

A vulnerability scan flags ESXi hosts with known CVEs exploitable remotely.

Root cause analysis

Patch management is critical not just for security but for stability. When patches for ESXi/vCenter or firmware/drivers are delayed, hosts may run with unsupported combinations, leading to instability (storage path failures, driver mismatches) and security risk (vulnerability exploitation). For example, ransomware campaigns have targeted ESXi hypervisors with known vulnerabilities.

Troubleshooting steps

Use Lifecycle Manager or equivalent to audit host patch/firmware compliance.

Run vulnerability scan on hosts for known CVEs (e.g., ESXi remote code execution).

Check host logs for warnings: driver mismatch, storage path errors, time sync warnings.

Validate host time sync (NTP) and guest OS clock stability across cluster.

Solution

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

Use test/staging hosts before production, validate before wide rollout.

Automate compliance checks and remediation via tools (Lifecycle Manager baselines).

Monitor host health and vulnerability compliance continuously; set alerts for non-compliance.

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Scenario 26: DNS / Name Resolution Failures in vSphere Infrastructure

The story

An enterprise virtualisation environment using VMware vSphere began suffering intermittent host disconnects from the management server, failure of vMotion and HA events, and unexpected authentication failures. Investigation revealed that the root cause was DNS mis-configuration — reverse lookup zones missing, outdated host records, and inconsistent FQDN resolution among vCenter, ESXi hosts and storage arrays. In fact, a TechTarget article points out that improperly configured DNS is a subtle but frequent source of VMware problems.

Symptoms

ESXi hosts show “Disconnected” or “Not responding” in vCenter.

vMotion or DRS operations fail with host communication errors.

HA fails to restart VMs because host cannot communicate or recognise names.

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

Root cause analysis

vSphere management, clustering, and infrastructure services rely heavily on reliable name resolution. If ESXi hosts can’t properly resolve the vCenter FQDN (or vice versa), management traffic fails. Similarly, storage arrays, NFS/iSCSI targets, or switches may rely on hostnames. As per documentation, an inaccessible or unstable vCenter may trace back to storage or network issues — but DNS is often the silent culprit.

Troubleshooting steps

On vCenter and each ESXi host, check hostname (FQDN) configuration and verify it matches DNS entries.

From each host, test ping and nslookup to vCenter FQDN and IP; check both forward and reverse lookup.

Review DNS zones: ensure reverse zone exists, host records are correct.

Inspect log files on hosts and vCenter for “lookup failed” or “unknown host” errors.

If storage is impacted, also test name resolution to storage controllers/targets.

Solution

Standardise the naming: ensure vCenter, hosts and storage use FQDNs, and that DNS forward/reverse zones are correct.

Update /etc/hosts (or equivalent) temporarily if DNS errors persist while full fix is applied.

Establish monitoring/alerting on DNS resolution failures for infrastructure components.

Incorporate DNS checks in your holiday/maintenance checklist: before upgrades or host additions.

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Scenario 27: VMFS/Datastore Version Mismatch – Migration Fails Post Upgrade

During a data-centre consolidation, the team upgraded some ESXi hosts to the latest version but left certain datastores at legacy VMFS format. After host upgrade, when trying to migrate VMs between hosts/datastores, they encountered errors and failed migrations. The root cause was the VMFS version incompatibility with the newer host version.

Symptoms

VM migrations (Storage vMotion or simple vMotion) fail with errors like “Incompatible datastore version” or “host cannot access datastore”.

Hosts report datastore compatibility warnings in vCentre.

Some services inside VMs show I/O errors or warnings.

Root cause analysis

VMFS (Virtual Machine File System) versions are tied to ESXi versions. If a host supports a newer VMFS, but tries to access older version or features that are no longer supported, compatibility issues can occur. Documentation emphasises checking datastore version compatibility when adding or upgrading hosts.

Troubleshooting steps

On each datastore, check VMFS version in vSphere (Datastores → details).

On hosts entering the cluster, check supported VMFS versions and compatibility list.

For failed migrations, inspect error message: if it references datastore version or compatibility, that's a clue.

Review host logs for storage or datastore access errors.

Solution

Upgrade the VMFS version/downgrade hosts accordingly: convert datastores to a supported VMFS version if needed.

Before adding upgraded hosts, inventory datastore versions and plan migration or upgrade of datastores.

Create policy: no new hosts added until datastore compatibility confirmed.

Monitor datastore version mismatch warnings in vCenter and remediate proactively.

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Scenario 28: Inadequate Free Space on Host/Datastore Causing vCenter Appliance Instability

A vCenter Server Appliance (VCSA) started exhibiting intermittent instability: UI sluggishness, occasional service restarts, and management tasks failing. Investigation found that the VCSA’s datastore was nearly full. The underlying host logs showed storage latency and write errors on the LUN hosting VCSA. VMware’s knowledge base article specifies that erratic vCenter behaviour can be caused by storage issues on the LUNs hosting the VM.

Symptoms

vCenter Appliance unresponsive or slow; UI times out.

Hosts show management communication failures with vCenter.

Logs on vCenter: file system errors, VMware services failing to start.

Root cause analysis

vCenter is critical infrastructure — if its storage (disk/VMFS) is mis-behaving (due to full capacity, I/O errors, path issues) the management layer can fail. The KB article explicitly links vCenter instability with storage issues on the LUN. Even if host CPU/memory look fine, storage pressure can cause cascading issues.

Troubleshooting steps

Identify the datastore/volume hosting the VCSA VM.

On host, check esxcli storage vmfs extent list to find NAA ID and underlying LUN.

Support Portal

Check free space on the datastore; evaluate I/O errors in /var/log/vmkernel.log or /var/log/vobd.log.

On VCSA VM, use console or SSH to inspect disk usage (e.g., df -h) and service statuses (service-control --status --all).

Solution

Free up space on the datastore: delete unused snapshots, old logs, or expand the datastore if necessary.

Move non-critical VMs off the same datastore to reduce competition.

Ensure storages servicing the VCSA meet performance and capacity requirements (I/O, latency, headroom).

Monitor VCSA datastore free space and I/O health proactively; alert when thresholds crossed.

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Scenario 29: Legacy Firmware on Storage Controller Prevents VM Migration After Host Upgrade

After upgrading ESXi hosts to the latest supported version, a virtualisation team attempted to vMotion VMs off older hosts but found some workloads failed with storage protocol or driver errors. On inspection, the storage array’s controller firmware was outdated and not certified for use with the newer host version. This mismatch prevented full functionality of Storage vMotion and features like snapshot removal.

Symptoms

vMotion or storage migration tasks fail with messages referencing “unsupported driver/firmware”.

Hosts log errors about storage path, SCSI commands not optimised, or controller compatibility.

Some VMs stuck in “Migrating” state or paused.

Root cause analysis

VMware maintains compatibility lists for storage controller firmware and drivers. When host software is upgraded but storage array firmware lags behind, incompatibilities emerge. Such issues have been flagged in common-issues guides (e.g., unsupported driver versions cause VM downtime).

DNSstuff

Troubleshooting steps

Review error logs in vCenter/hosts referencing migration failure and identify driver/firmware warnings.

On storage array vendor’s portal, check compatibility matrix for host version vs firmware version.

Inventory storage controller firmware and driver on hosts (via esxcli storage core adapter list etc).

Test migration of a smaller VM to isolate if all migrations fail or only certain ones.

Solution

Update firmware/drivers on storage array and host adapters to match VMware’s compatibility list.

Before host upgrades, validate storage compatibility matrix and plan firmware updates ahead.

For large environments, stage host upgrades together with storage firmware maintenance.

Document hardware/firmware inventory and compatibility status as part of upgrade risk assessment.

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Scenario 30: VM Sprawl & Idle VMs Causing Resource Waste and Impact on Performance

A midsize business saw a rapid growth of VMs over time — many of them idle, under-utilised, but still registered, powered on, and consuming resources (memory, storage, licensing). Because resources were tied up, performance of other critical VMs suffered (particularly memory/CPU contention). The issue was compounded by lack of lifecycle management and monitoring.

Symptoms

Many VMs show little CPU/IO activity but are powered on.

Hosts have high memory consumption though workload seems modest.

Storage is consumed by idle VMs (including snapshots) and datastore free space slowly declines.

Performance issues in business-critical VMs despite seeming headroom.

Root cause analysis

VM sprawl — unmanaged growth of VMs — leads to waste in compute, memory, storage, and licensing. These idle VMs still consume ballooning memory allocations, keep snapshots, and even when idle, add to host overhead (management traffic, backup, monitoring). Articles on VMware issues note “improper configuration, resource constraints, hardware incompatibilities” often contribute to performance issues.

Troubleshooting steps

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

Check snapshot usage and age for these idle VMs.

Review host and resource pool usage; correlate idle VMs to resource consumption.

Identify VMs still powered on but no longer needed or can be consolidated.

Solution

Implement VM lifecycle policy: regularly review powered-on VMs, idle ones should be shut down or decommissioned.

Use monitoring tools to identify idle VMs and snapshot sprawl.

Reclaim resources: power off or delete idle VMs, remove passages and large snapshots.

Monitor resource usage and set thresholds/alerts for idle VM count, snapshots older than X days.