You have an SQL server with a vast number of SQL databases (100+) in one SQL instance.
Backup of this server fails with: VSS writer 'SqlServerWriter' with class ID 'A65FAA63-5EA8-4EBC-9DBD-A0C4DB26912A' has failed to process the snapshot. To troubleshoot VSS issues, download and run Acronis VSS Doctor available at https://www.acronis.com/en-us/personal/vss-diagnostic-free-tool/
Too many databases (<quantity of databases>) of SQL Server instance 'MSSQLSERVER' are selected for backup.
1. Set for SQL instance Maximum worker threads to total number of databases * 2. For example, you have 500 databases. Then set Maximum worker threads to 1000.
Using SQL Server Management Studio
- In Object Explorer, right-click a server and select Properties.
- Click the Processors node.
- In the Maximum worker threads box, type or select 1000.
- Connect to the Database Engine.
- From the Standard bar, click New Query.
- Copy and paste the following command set into the query window and click Execute.
USE AdventureWorks2012 ;
EXEC sp_configure 'show advanced options', 1;
EXEC sp_configure 'max worker threads', 1000 ;
2. Restart SQL server instance.
Run backup again. Is should work fine now.