ReFS Known Issues, Considerations, and Limitations

Backup Job retention enforcement with ReFS-based backup repositories leads to the following issues on the repository server:

• The repository server becomes unresponsive or crashes.
• I/O performance on the repository server is reduced significantly.
• The repository server experiences high memory usage.

These issues can, in turn, lead to unexpected job termination.

• 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 take place, 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

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. 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.
• Reference: Repository Server Sizing Best Practices
• 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 can potentially include bloatware).