SQL - A VSS critical writer has failed. Writer's state: [VSS_WS_FAILED_AT_PREPARE_SNAPSHOT]

KB ID: 1915
Product: Veeam Backup & Replication
Version: All
Published:
Last Modified: 2016-02-17

Challenge

When attempting to backup a SQL server that is hosting a significant amount of  databases the following error is thrown:
 
Unable to release guest. Error: Unfreeze error: [Backup job failed. Cannot create a shadow copy of the volumes containing writer's data. A VSS critical writer has failed. Writer name: [SqlServerWriter]. Class ID: [{}]. Instance ID: [{}]. Writer's state: [VSS_WS_FAILED_AT_PREPARE_SNAPSHOT]. Error code: [0x800423f4].]
Error: Unfreeze error: [Backup job failed. Cannot create a shadow copy of the volumes containing writer's data. A VSS critical writer has failed. Writer name: [SqlServerWriter]. Class ID: [{}]. Instance ID: [{}]. Writer's state: [VSS_WS_FAILED_AT_PREPARE_SNAPSHOT]. Error code: [0x800423f4].]

Cause

In SQL Server, the snapshot backup of each database uses five threads in the Sqlservr.exe process. Additionally, other activities may also use threads in the Sqlservr.exe process. Depending on the configuration of SQL Server, the available threads may be used up if you create a snapshot backup of many databases at the same time.
 
It is possible to process the VM in a crash-consistent manner by disabling Application-Aware Image Processing within the job.

Solution

It is advised to create another SQL Server and move the databases that are causing failure to the other SQL server.
In certain scenarios changing the max worker threads Server Configuration Option may help negate the issue. However, it is advisable to contact Microsoft support for verifying this step.
Please refer to the following articles for details:
https://support.microsoft.com/en-us/kb/943471
http://blogs.msdn.com/b/psssql/archive/2009/03/03/how-it-works-sql-server-vdi-vss-backup-resources.aspx
https://msdn.microsoft.com/en-us/library/ms190219.aspx?f=255&MSPPError=-2147217396
https://support.microsoft.com/en-us/kb/2157129


 

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