Unable to exclude files from snapshot: Shadow Copy Optimization Writer is not available

KB ID: 2076
Product: Veeam Endpoint Backup;Veeam Agent for Microsoft Windows
Version: 1.x, 2.x
Last Modified: 2017-04-14


During a backup job Veeam Endpoint Backup or Veeam Agent for Windows returns the following warning:

Unable to exclude files from snapshot: Shadow Copy Optimization Writer is not available


The issue is caused by the Microsoft Shadow Copy Optimization Writer failure, which Veeam Endpoint Backup displays.

This issue with MS Copy Optimization Writer availability is sporadic. So far we were not able to narrow it down to a specific configuration. It may or may not affect backups within the same chain without any apparent changes predating the symptoms.

In such cases the Application Event Log on the workstation in question may contain entries similar to the one below:

Source: VSS
Event ID: 8193
Level: Error

General: Volume Shadow Copy Service error: Unexpected error calling routine ConvertStringSidToSid, The security ID structure is invalid.

 OnIdentify event
 Gathering Writer Data

 Execution Context: Shadow Copy Optimization Writer
 Writer Name: Shadow Copy Optimization Writer


The available workaround is described in the following Technet post. Keep in mind, that there is no guarantee, that this workaround will help in your specific scenario.

Since the root case is on the Microsoft side, it is best to involve Microsoft Support if you need a permanent solution. We can assist you with the collection of diagnostic information for Microsoft and participate in the communication with them. To involve Veeam Support, please, open a support case as described below.

More Information

If you have further questions, open a support case as follows:

  1. Right-click the Veeam Endpoint Backup / Veeam Agent for Windows icon in the system tray and select Control Panel.
  2. Click the Support link at the top of the window.
  3. Click Technical Support to submit a support case to the Veeam Support Team directly from the product.
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