DPM 2012 Backing up a VM on Server 2012 Hyper-V CSV Host - Not Working with Hardware VSS

Question

Hi All,
I'm trying to backup a VM on a 2012 Cluster. I can do it by using the system VSS provider, but when I try to use the hardware provider, (Dell equalogic) it doesn't work. DPM will sit for a while trying and then report a retryable VSS error. 
The only error I'm seeing on the Host is the following:
Event ID 12297Volume Shadow Copy Service error: The I/O writes cannot be flushed during the shadow copy creation period on volume \\?\Volume{3312155e-569a-42f3-ab3a-baff892a2681}\. The volume index in the shadow copy set is 0. Error details: Open[0x00000000, The operation completed successfully.
], Flush[0x80042313, The shadow copy provider timed out while flushing data to the volume being shadow copied. This is probably due to excessive activity on the volume. Try again later when the volume is not being used so heavily.
], Release[0x00000000, The operation completed successfully.
], OnRun[0x00000000, The operation completed successfully.
Operation:
Executing Asynchronous Operation
Context:
Current State: DoSnapshotSet
I don't know where to go from here - There is no activity on the CSV (this is the only VM on it, and both the CSV and VM were created specifically for testing this issue
Does anyone have any ideas? I'm desperate. 
Update:
Ok, so I can Take DPM out of the picture. Trying to do a snapshot from the Dell Auto-Snapshot manager, I get the same errors. But I also get a bit more information:
Started at 3:02:47 PM
Gathering Information...
Phase 1: Checking pre-requisites... (3:02:47 PM)
Phase 2: Initializing Smart Copy Operation (3:02:47 PM)
Adding components from cluster node SB-BLADE01
Adding components from cluster node SB-BLADE04
Adding components from cluster node SB-BLADE02
Retrieving writer information
Phase 3: Adding Components and Volumes (3:02:52 PM)
Adding components to the Smart Copy Set
Adding volumes to the Smart Copy Set
Phase 4: Creating Smart Copy (3:02:52 PM)
Creating Smart Copy Set
An error occurred:
An error occurred during phase: Creating Smart Copy
Exception from HRESULT: 0x80042313.
Creating Smart Copy Set
An error occurred:
An error occurred during phase: Creating Smart Copy
Exception from HRESULT: 0x80042313.
An error occurred:
Writer 'Microsoft Hyper-V VSS Writer' reported an error: 'VSS_WS_FAILED_AT_FREEZE'. Check the application component to verify it is in a valid state for the operation.
An error occurred:
One or more errors occurred during the operation. Check the detailed progress updates for details.
An error occurred:
Smart Copy creation failed.
Source: Creating Smart Copy Set
An error occurred:
An error occurred during phase: Creating Smart Copy
Exception from HRESULT: 0x80042313.
An error occurred:
Writer 'Microsoft Hyper-V VSS Writer' reported an error: 'VSS_WS_FAILED_AT_FREEZE'. Check the application component to verify it is in a valid state for the operation.
An error occurred:
One or more errors occurred during the operation. Check the detailed progress updates for details.
Error: VSS can no longer flush I/O writes.
Thanks,
John

Answer 1

I had a similar issue with an environment that had previously been working with the Dell HIT configured correctly. As we added a third node to the cluster I began seeing this problem.
In my case I had the HIT volume max sessions per volume at 6 and maximum sessions per volume slice set to 2 and the CSV was using a LUN/Volume on the SAN that was split across 2 members.
When the backup takes place and Dell HIT is configured to use SAN snapshots the vss-control iSCSI target is used which in my case exceeded my limits for maximum connections per volume as I'm using 2 paths per Hyper-V node with MPIO (this is my
current theory).
Once I'd modified these settings I could then back up the VHD's on that CSV again.
Hope this helps.