Backup DFS Replication

Hello ​@SSchmidt  
 

The best practice for backing up a Windows Server with DFS Replication (DFSR) using the Commvault Windows File System Agent is:

• Only back up read-only DFSR members.
• Never back up or restore computers running DFSR on read-write members in a production environment.

Reason

The DFSR database and other Windows multi-master databases do not support snapshots. Backing up or restoring read-write DFSR members can cause replication failures and data inconsistency.

Procedure

1. Identify Read-Only DFSR Members:

• Ensure the server you plan to back up is configured as a read-only DFSR member.

1. Configure the Windows File System Agent:

• Install and configure the agent on the read-only DFSR server.
• Set up your backup jobs as usual.

1. Exclude Read-Write Members:

• Do not configure backups for DFSR servers that are read-write members.

If Restore Is Needed

• If you must restore a DFSR server and it is not read-only, work with Microsoft Support to repair the DFSR database and restore replication functionality.

Reference

For more information, see the Microsoft KB article:

Distributed File System Replication (DFSR) no longer replicates files after restoring a virtualized server's snapshot

and Commvault support article:

https://kb.commvault.com/article/54466

Summary:

Back up only read-only DFSR members with the Windows File System Agent. Never back up or restore read-write DFSR members in production to avoid DFSR replication issues.

Documentation Links

• Commvault Support Article 54466
• Microsoft DFSR Restore KB

Regards,

Kalaivanan. 

Hi,

thanks for your quick reply. u have some more questions :) 

What is regarding VSA Backup is that fine to run VSA Backups from both nodes ? Or should we run crash consistent on primray node and normal vsa backup on readonly node

If i run Windows FIle Backup only on the read only node i have the problem when the windows replication is getting stucked i backup old data. 

 Hi ​@SSchmidt 

Please find the updated response. 

It is recommended to backup DFS servers using Windows file system agent based backup and not with VSA.
 

• DFSR’s multi‑master database does not tolerate image/snapshot restores, using VSA (image‑level) snapshots or virtual machine snapshot restores of read‑write DFSR members can break replication and leave the server non‑replicating. Commvault therefore recommends not to back up or restore read‑write DFSR members with VSA.
• VSA backups operate at the image/snapshot level and can restore the on‑disk state of the DFSR database without the coordinated multi‑master hygiene DFSR requires, leading to replication failures.
• Backup operations also interact with VSS/DFSR writers (Commvault may pause DFSR during backup); while this is expected behavior during backup, restoring a read‑write replica to a prior point can leave replication in an unrecoverable state unless handled by Microsoft support.

Reference Comvmvault article: https://kb.commvault.com/article/?id=54466

• Best Practice:
  Only run Windows File System Agent backups on the read-only DFSR node.
• Limitation:
  If DFS replication is stuck or lagging, the backup on the read-only node may not reflect the latest data from the primary. This is a limitation of the DFSR architecture, not Commvault.

Reference MS article: https://learn.microsoft.com/en-us/troubleshoot/windows-server/networking/distributed-file-system-replication-not-replicate-files#cause