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How to diagnose a vMotion failure

This BAOI guide provides a structured method for diagnosing vmotion failure without multiplying unnecessary changes.

TopicVMware →
⌚ About 2 min read
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VMware. Intermediate. 15-30 min

This BAOI guide provides a structured method for diagnosing vmotion failure without multiplying unnecessary changes.

Avant de commencer : adaptez toujours les commandes et manipulations à votre environnement. Sur un système de production, prévoyez une backup ou un retour arrière lorsque l’action peut modifier la configuration.

Étapes à suivre

  1. 1

    Set perimeter

    Identify the equipment, service, affected users and start time.

  2. 2

    Collect Elements

    Record the exact messages, logs and useful settings.

  3. 3

    Test methodically

    Start with the basic dependencies before the application components.

  4. 4

    Apply correction

    Change only the identified parameter or component.

  5. 5

    Validate

    Rewrite the full scenario and document the result.

À retenir

  • Keep the initial values for a backwards.
  • Avoid multiple simultaneous changes.
  • Compare with a functional configuration when possible.
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Technical deep dive

VMware: storage, vMotion network and CBT must be validated by layer

Technical checkpoints

  • A datastore can fill due to snapshots, thin provisioning, logs or guest growth; provisioned capacity and actual consumption differ.
  • vMotion depends on VMkernel networking, routing/VLAN, MTU
  • CBT accelerates incremental backups, but invalid/corrupt CBT should be handled using the backup vendor procedure, not by arbitrarily deleting ctk files.

Targeted checks

For vMotion, test source-to-destination VMkernel using the real MTU; for storage, identify snapshots and growing files.

vmkping -I vmkX -d -s 8972 <peer>
esxcli storage filesystem list

Topic-specific pitfalls

  • Deleting a snapshot from datastore browser can break the chain; use Snapshot Manager/Consolidate.
  • A migration that works with small packets can still fail when jumbo frames are mismatched.

How to validate

  • The datastore regains headroom and no abnormal snapshot/consolidation remains.
  • vMotion succeeds with expected VMkernel/MTU and CBT backups become consistent again.

Operational context

A vMotion failure should be separated into vMotion VMkernel reachability, MTU/VLAN consistency, host compatibility and VM-specific constraints. Start with the migration network rather than repeatedly retrying the task.

Step-by-step checks

  1. Confirm each ESXi host has the intended VMkernel adapter enabled for vMotion and that the source/destination networks match.
  2. Test VMkernel-to-VMkernel reachability using the exact vMotion interfaces; if jumbo frames are configured, validate the full MTU path.
  3. Review the vCenter task/event error and vmkernel logs for the failing migration timestamp.
  4. Check CPU/EVC compatibility, datastore accessibility, active snapshots and device mappings that can prevent migration.

Useful verification commands

Use commands only on systems you administer and capture the read-only output before making a configuration change.

vmkping -I vmkX <destination-vmotion-ip>
vmkping -I vmkX -d -s 8972 <destination-vmotion-ip>

How to validate the result

Repeat a controlled migration of the affected VM and confirm the task completes without network retries, compatibility warnings or a fallback to an unintended path.

Evidence to keep

Keep source/destination hosts, VMkernel IPs, MTU, vCenter task ID/error, relevant log lines and the successful retest timestamp.

Frequently asked question

Does a successful normal ping prove vMotion is healthy?

No. The test must use the vMotion VMkernel path, and a standard-size ping does not prove a jumbo-frame path when MTU 9000 is configured.

Related BAOI resources: IT tools · procedures · IT dictionary.

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