ReFS Known Issues, Considerations, and Limitations

Configuration Related

• Do not use ReFS with iSCSI or FC SANs unless explicitly supported by the hardware vendor.
• ReFS supported configurations must use Windows Server Catalog certified hardware.
• ReFS does not support SAN storage features such as thin provisioning, TRIM/UNMAP, and ODX.
• Do not use deduplication in combination with ReFS block cloning.
• Ensure scheduled Data Integrity Scans do not overlap with your backup window.
• ReFS relies on flush durability, meaning that if filesystem metadata write operations occur, they must be consistently flushed to disk. If a storage destination is used where a cache acknowledges writes before they are written to disk, for example, by a RAID controller or NAS, and those metadata writes then do not make it to disk due to a power failure, the filesystem may become corrupted.
• There were several Windows Updates• Server 2012 R2 - KB5009624
  • Server 2019 - KB5009557
  • Server 2022 - KB5009555 that broke ReFS functionality with removable media. Microsoft does not support ReFS on removable media. However, Microsoft has released out-of-band updates to restore functionality, but only for ReFS v2 and higher. For more information, review: Veeam Community Discussion: ReFS issues with latest Windows Server Updates

OS Notes

• While Microsoft does support booting from ReFS volumes under particular circumstances involving Azure confidential VMs, this configuration is not supported by Veeam Agent for Microsoft Windows. Although it is technically possible to configure Windows to boot from an ReFS volume, doing so may lead to stability issues with Veeam Agent for Microsoft Windows. For example, attempting to back up an ReFS boot volume using Veeam Agent for Microsoft Windows has a high probability of causing a BSOD.
• Veeam always recommends keeping all systems fully patched with the latest Windows Updates for best performance and security.

Hardware

• The backup repository server must meet minimum system requirements.
• For environments where a single server handles multiple roles (aka All-in-One Installation), ensure that the server has enough RAM based on the combined requirements of all roles assigned to it.
   

3rd Party Software

Uninstall the following 3rd party software, as these have been reported to cause ReFS instability 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 (instead of using an image provided by the server vendor, which may include bloatware).