User Tools

Site Tools



Ahsay Backup Software

Backup Set Types

Supported Storage

Features in OBM / ACB

Features in CBS

Brand and Customize



Performance Testing

FAQs and Known Issues

Can't Find What You Need?


ISSUE: Cannot start shadow copy (VSS_E_WRITERERROR_NONRETRYABLE) (MS SQL server with large number of databases)

Article ID: 8086
Reviewed: 10/11/2020

Product Version:
AhsayOBM: or above
OS: Windows

Problem Description

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:

No. Type Timestamp Log
* ... ... ...
* info ... [Start] Backing up database...
* erro YYYY/MM/DD hh:mm:ss 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:

    • In the Object Explorer, right click a server and select Properties.

    • Click the Processors node.

    • In the Max worker threads box, type or select a value for the max worker thread.

    For more details, refer to the following article:

    Please consult with an experienced database administrator or certified SQL Server technician before making any change to the maximum worker threads.


mssql, sql, worker threads, max, databases

public/8086_issue/vss_e_writererror_nonretryable.txt · Last modified: 2020/11/12 16:37 by edward.chan