⌚ About 2 min read

VMware. Intermediate. 15-30 min

This BAOI guide provides a structured method for diagnosing vmware cbt 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

Set perimeter

Identify the equipment, service, affected users and start time.
2

Collect Elements

Record the exact messages, logs and useful settings.
3

Test methodically

Start with the basic dependencies before the application components.
4

Apply correction

Change only the identified parameter or component.
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.

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
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

Changed Block Tracking problems affect incremental backup efficiency and can require a controlled CBT reset. First prove the VM and backup-chain state, then follow the backup vendor and VMware-supported reset sequence instead of deleting tracking files blindly.

Step-by-step checks

Confirm the backup error explicitly points to CBT/CTK rather than a generic snapshot or datastore failure.
Check whether the VM has pending snapshot consolidation, recent disk topology changes or a restore/migration event that could invalidate CBT state.
Verify CBT configuration for the VM and virtual disks and compare it with the backup product requirements.
If a CBT reset is required, schedule it in a maintenance window and use the supported sequence so the next backup can rebuild tracking safely.

Useful verification commands

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

vim-cmd vmsvc/getallvms

How to validate the result

The next backup must complete without CBT errors, create a consistent new tracking baseline and subsequent incremental jobs must process changed blocks normally.

Evidence to keep

Record VM ID/name, backup job/session ID, exact CBT error, snapshot/consolidation state and first successful full/incremental result after remediation.

Frequently asked question

Can I just delete CTK files from the datastore?

Do not treat direct CTK-file deletion as a generic fix. Use the supported CBT reset procedure for the VM and backup product because an unsafe reset can invalidate backup assumptions.

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