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ReFS. Known issues

KB ID: 2792
Product: Veeam Backup & Replication
Published: 2018-11-06
Last Modified: 2020-08-13


Backup job retention processing on ReFS-based backup repositories leads to following issues:
  1. Repository server becomes unresponsive or crashes.
  2. I/O performance on the server is reduced significantly.
  3. The server experiences high memory usage.
These issues can in turn lead to unexpected jobs termination.


As described in Microsoft article KB4016173 the root cause resides in the ReFS metadata management logic of the Windows OS system memory manager.


Operating System
Use the following OS versions, which include fixes to the ReFS metadata management logic:

  • Windows Server 2019 (requires Veeam Backup and Replication 9.5 Update 4 or later)
  • Windows Server 2016 patched to at least September 2018 updates (KB4343884 or later)
  • Windows 10 Pro for Workstations

Note: refs.sys driver version should be at least 10.0.14393.2457 or later. However, for best performance and security, we always recommend keeping all systems fully patched with the most recent Windows Updates .

Backup repository must meet minimum system requirements. In particular, pay attention to the following in case of all-in-one backup appliances:

  • CPU: ensure at least 1 core per each concurrent backup proxy task AND at least 1 core for each two concurrent repository tasks are available.
  • RAM: ensure the repository server has enough RAM (at least the sum of RAM requirements for each individual Veeam component installed on the server).
  • Storage: use 64KB cluster size when formatting the ReFS volume.

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: To ensure no conflicting software is present, we recommend deploying Windows OS using the original ISO file from Microsoft (as opposed to using an image provided by the server vendor, which can potentially include bloatware).

More information

We continue to collaborate with Microsoft ReFS development team closely on ReFS improvements. To monitor the current status, please refer to this Veeam forums discussion.
KB ID: 2792
Product: Veeam Backup & Replication
Published: 2018-11-06
Last Modified: 2020-08-13

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