ReFS. Known issues

KB ID: 2792
Product: Veeam Backup & Replication
Last Modified: 2019-02-15


Backup and Backup Copy synthetic operations such as retention (merging) or Synthetic Full creation on ReFS based repositories could lead to following issues:

  1. Memory exhaustion on Repository Servers with ReFS
  2. Synthetic operations take a considerable amount of time
  3. The Repository server becomes unresponsive or has significantly reduced performance
All of the above could lead to unexpected/faulty backup/backup copy jobs termination.


As described in Microsoft article KB4016173 the root cause resides in the existing design of ReFS metadata management.


After performing many tests across multiple installations, our RnD and Solution Architects have found the below recommendations to be most effective for resolving the symptoms described in the "Challenge" section:

Operating System

Use the following OS versions to avoid any known ReFS issues described in “Challenge” section:
  • Windows Server 2019 (not officially supported until Veeam Backup and Replication 9.5 Update 4. Lab use only)
  • Windows Server 2016 patched to at least September 2018 updates (KB4343884 or later)
  • Windows 10 Pro for Workstations
Note: refs.sys driver file should be 10.0.14393.2457 or later
Veeam and Microsoft recommend keeping all systems fully updated with the most recent Windows Updates for best performance.


Backup repository should meet minimum system requirements. In particular:
  • CPU: at least 1 core per each concurrent backup proxy task and at least 1 core for each two concurrent repository tasks recommended
  • RAM: Backup repository server running other backup roles should have an appropriate amount of RAM for each role
  • Storage: 64K ReFS volume formatting is recommended

3rd Party Software

Uninstall the following 3rd party software that have been reported to cause ReFS stability and/or performance issues:
  • Antivirus software (except Windows Defender)
  • Microsoft Configuration Manager Client
Note: general recommendation is to run an unmodified image of Windows installed from original ISO or MSDN resource to ensure no conflicting or problematic software is installed.

More Information

We continue to closely collaborate with Microsoft ReFS team on improving stability and performance of ReFS. To monitor current state please refer to our forum discussion.

Please be aware that we’re making changes which will restrict access to product updates for users without an active contract.


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