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The backup of an Exchange server VM fails with:
Unfreeze error:[Backup job failed] Cannot create shadow copy of the volumes containing writer’s data A VSS critical writer has failed. Writer name: [Microsoft Exchange Writer]. Class ID: [{76fe1ac4-15f7-4bcd-987e-8e1acb462fb7}]. Instance ID: [{0db23250-4d1e-42c1-8d14-2be32f448184}]. Writer's state: [VSS_WS_FAILED_AT_FREEZE]. Error code: [0x800423f2].]
If you run the command ‘vssadmin list writers’ on the Exchange server after the job fails, typically you will see an Exchange Writer has failed because of a timeout error (error code 9).
Starting in Veeam Backup & Replication v8
To overcome this VSS limitation, Veeam Backup & Replication utilizes the Microsoft VSS persistent snapshots technology for backup of Microsoft Exchange VMs. If Microsoft Exchange fails to be frozen within the allowed period of time, Veeam Backup & Replication automatically fails over to the persistent snapshot mechanism. To learn more about this new feature please read:
https://helpcenter.veeam.com/docs/backup/vsphere/persistent_snapshots.html
"VSSControl: Failed to freeze guest, wait timeout"
Refers to the limit imposed by Microsoft VSS writers on the duration of a freeze. This timeout is not configurable. Veeam uses VSS to freeze applications immediately prior to creating the VMware snapshot, and then sends the thaw command as soon as snapshot creation is complete. VSS will only hold a freeze on the writers for up to 60 seconds (20 for Exchange), so several steps must fit within this timeframe:
1 If a network connection to the guest OS is not available, VIX API will be used, which introduces additional latency.
2 These steps should usually be near-instantaneous, but if the vCenter is heavily loaded or has a high latency to the ESXi hosts, the delay may be significant.
This issue is an infrastructure issue that can be difficult to narrow down. The following is a comprehensive list of resolutions that customers have used to resolve the issue:
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