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Either of the following errors occurs in the job statistics:
"VSSControl: Failed to prepare guest for freeze, wait timeout 900 sec."
"VSSControl: Failed to freeze guest, wait timeout"
These errors look similar but their causes are unrelated.
"VSSControl: Failed to prepare guest for freeze, wait timeout 900 sec"
Refers to VSS preparation, which consists largely of enumerating VSS writers, their components, and associated files and volumes. The timeout may be exceeded because of performance limitations of the VM guest, or because a specific writer is enumerating a very large number of files. This timeout is configurable.
"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.
Note:
You can change this timeout by modifying the value in the registry of the server where Veeam Backup & Replication is installed as follows:
Notes:
Identification of Problem Writer:
diskshadow /l <path to output file>.txt list writers detailed
Both errors are related to Application Aware Image Processing. As a temporary workaround, you can disable AAIP in order to obtain crash-consistent backups. For more information, consult the user guide overview of Transaction Consistency.
Overview of Processing a Backup Under VSS has a visual explanation of the freeze timeout (the green box).
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