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When performing either a scheduled or manual MS SQL database backup job, where there are a large number of databases selected in the backup source. The following backup error is received in the backup report:
|*||info||...||[Start] Backing up database...|
Cannot start shadow copy, reason =The writer operation failed because of an error that might
recur if another shadow copy is created. (VSS_E_WRITERERROR_NONRETRYABLE)
The error message is returned by MS SQL VSS writer, suggesting that there were insufficient number of worker threads configured on the MS SQL Server to support the backup all databases selected for backup.
A MS SQL Server databases backup job using VSS requires three worker threads per database. For example, a 64 bit MS SQL server with 4 CPUs is automatically configured with 512 work threads, which implies that the maximum number of databases that can be selected for backup is 170.
Please refer to the Limitations and Restrictions section in the following article for more details:
To resolve this issue, either:
1. Create additional backup sets (to be performed at different time) for the excess databases.
2. Increase the maximum number of worker threads on the MS SQL Server.
To configure the max worker threads option:
MS SQL Server, worker threads, max, databases