vSAN 'Disk format version' alarm after upgrade to ESXi 8.0 Update 3

Products

• VMware vSAN

Issue/Introduction

Following an upgrade of ESXi hosts to version 8.0 Update 3, the vSAN Skyline Health service reports a 'Disk format version' health alarm and the cluster alerts vSAN Cluster alarm 'Disk format version'.

• The status may be Yellow (Warning) or Red (Alert).
• Under Health Details, the message indicates: vSAN cluster expected format version is 20.0, which is the highest supported format version...
• Current disk format version is typically reported as 15.0 or lower.
• Secondary alerts for 'vSAN disk balance' may also appear due to the version mismatch.

Environment

vSAN 8.0 U3
vSAN On Disk Format below version 20

Cause

When ESXi hosts are upgraded to 8.0 Update 3, vSAN supports a new On-Disk Format (ODF) Version 20. While legacy formats (like Version 15) remain compatible for data access, vSAN requires a metadata upgrade to Version 20 to enable the latest features, performance optimizations, and efficient data rebalancing across the cluster. A version mismatch triggers the health alarm to ensure administrative awareness.

Resolution

To resolve the alarm, you must perform an automated rolling upgrade of the vSAN on-disk format at the cluster level.

Prerequisites

1. Verify Object Health: Navigate to Monitor > vSAN > Skyline Health. Ensure the 'Data Health' section shows no inaccessible objects. If objects are inaccessible, they must be resolved first (refer to KB 389599).
2. Maintenance Window: While the upgrade is typically non-disruptive (metadata-only for versions 3.0+), it is recommended to perform this during non-peak hours due to minor performance overhead during the rolling process.

Steps to Upgrade

1. In the vSphere Client, select the vSAN Cluster.
2. Navigate to Configure > vSAN > Disk Management.
3. Click Pre-check Upgrade. This verifies that the cluster is ready for the rolling update.
4. Once the pre-check returns a green status, click Upgrade.
5. Monitor the task progress. vSAN will automatically move from one host to the next, upgrading the disk groups.

Verification

Once the task completes:

1. Return to Skyline Health and click Retest.
2. Verify the 'Disk format version' check is now Green.
3. Confirm that all disk groups in Disk Management report Version 20.0.

Additional Information

Understanding vSAN on-disk format versions and compatibility

vSAN Health Service - Cluster Health - Disk format version

vSAN Health Service - Data Health - vSAN Object Health - inaccessible objects