VMware VM backup fails when MABS does not fall back to crash-consistent snapshot after quiesced snapshot failure

Products

• VMware vSphere ESXi

Issue/Introduction

• VMware virtual machine backups initiated from Microsoft Azure Backup Server (MABS) fail during snapshot creation.

• Backup logs report ApplicationQuiesceFault or errors indicating that the virtual machine could not be quiesced.

• Even when application quiescing is disabled at the VM, VMware Tools, and vCenter levels, the backup does not fall back to a crash-consistent snapshot.

• The backup job fails instead of completing successfully.

Environment

• VMware vSphere (all supported versions)

• Microsoft Azure Backup Server (MABS) version 14.0.30.0

• Windows-based VMware virtual machines with VMware Tools installed

Cause

MABS version 14.0.30.0 does not support fallback from a failed quiesced snapshot to a crash-consistent snapshot.
In this version, MABS always initiates snapshot creation requests with application quiescing enabled. If quiescing fails, the backup operation terminates instead of retrying with a non-quiesced snapshot.

Resolution

1. Make the changes as mentioned in the following article, VSS Quiesced Snapshot fails on virtual machine with independent disks

2. Upgrade Microsoft Azure Backup Server to version 14 Update 3 or later and enable the
   FailbackToCrashConsistentBackup registry parameter.

   This update introduces the capability for MABS to automatically fall back to crash-consistent snapshots when application quiescing fails.

   For configuration details, refer to Microsoft documentation:
   https://learn.microsoft.com/en-us/azure/backup/backup-azure-backup-server-vmware#applicationquiescefault

Additional Information

• MABS does not provide a user-configurable option to explicitly request non-quiesced snapshots.

• VMware processes snapshot requests exactly as received from the backup application and does not modify the snapshot type.

• The vmware.log on the virtual machine confirms that the snapshot request is initiated with quiescing enabled:

  TakeSnapshot start: 'SCDPM BACKUP_...',
quiesced=1

• Modifying VMware Tools configuration files or Windows VSS settings does not change the snapshot API call issued by MABS.