The Problem with Hardware VSS Providers and Cluster Technologies like CSV and DAG

In solutions like DAG and CSV you can have issues with VSS backups completing if you are attached to a SAN and using a hardware provider.
The reason for this is because the LUN needs to pause the processes accessing the LUN but if another server is the one in control  of data on that LUN its unable to do that on a single host.
Here are some details as well as ways to resolve this issue.

Scenarios:

1. CSV Issue

• Multiple Servers with a shared CSV Volume and VMS distributed across nodes may fail if you are using hardware VSS providers because it wants to snapshot the entire LUN but the node you are running the snap shot from doesn’t have access to all the VMS in order to pause them before committing the snapshot.

1. You can resolve this in one of 2 ways.
   1. Move all the VMs to a single node or host until the backup is completed.
   2. Disable or remove your hardware based VSS provider.

 

 

 

2. DAG Issue

This issue may come up not because you are sharing LUNS and have active data  on separate nodes (as above) but because you may use a separate provider for Active and Passive backups. When you try to backup a LUN that has both active and passive databases a hardware provider may try to use two different writers to snapshot the LUN. You can verify this by moving all active databases to one node to backup.

1. You can resolve this in one of 3 ways.
   1. Do not put multiple databases on a single LUN.
   2. Move all Databases to one node before running backup
2. 3. Disable you hardware based VSS provider

 

NOTE: Disabling your hardware provider will likely cause your backups to take much longer

References

• Disable Equal Logic VSS Writer – Run C:\Program Files\EqualLogic\bin>eqlvss /unregserver”
• Disable Hardware VSS in DPM – Add the following key to the registry [Software\Microsoft\Microsoft Data Protection Manager\Agent\UseSystemSoftwareProvider]
• How VSS Works
• If you know how to disable other providers please let me know and I will add it to this document!