Issues With Backing Up Too Many Volumes At Once

[FECV]

Hello,
I am encountering an issue with my backup setup and could use some assistance.

Environment:
• OS: Microsoft Failover Cluster (Server 2022)
• Storage: Dell Unity iSCSI SAN
• Backup Solution: Veeam Agent managed by VBR server (also acting as the proxy)
• Setup: 31 disks mounted on the failover cluster, many exceeding 64TB, serving as my primary file server.

Background: Historically, I've backed up each volume individually without issues, even for large volumes. However, one particularly large volume required splitting into 14 smaller volumes to improve backup times. A single backup job for these 14 volumes reduced the full backup time from 15 days to 4 days.
Issue: The backup job fails during the "Create VSS Snapshot" task when including 10 or more volumes. The error message is: “Failed to create VSS snapshot. Retrying…” The job usually fails after four attempts, but sometimes will succeed. I did manage to get all 14 volumes to backup one time.

Observations:
• Each volume can be backed up individually without issues.
• A job with up to 9 volumes completes successfully.
• When adding the 10th volume or more, the task usually fails during the VSS snapshot creation.
• During the snapshot creation attempts, I observe the snapshots being created on my SAN, which get mounted to the active cluster server. The failure occurs around the time all 14 disks are mounted, after which the snapshots are deleted.

Support's Perspective: Support is focusing on Veeam KB1794, which suggests increasing the space for VSS snapshots. However, I am skeptical since many disks exceed the Microsoft 64TB VSS limit, and I rely on storage snapshots using the Veeam Hardware VSS Provider. My understanding is that the Veeam Hardware VSS Provider is run against the mounted snapshot.

Question: I feel this is a timeout issue related to handling multiple (10 or more) volumes in a single job. How does increasing the VSS snapshot storage space help in this scenario? Any insights or similar experiences would be greatly appreciated.

Case Reference: #07298234

Thank you for your assistance.

[david.domask]

Hi Frederick,

Thank you for sharing the case number and for the detailed description. I'm not aware of any specific restrictions on the behavior you're seeing, and I would advise let's continue with the Support Case as I see that the last update was that the case is being prepared for escalation to the Advanced Support Team for review.

I do agree that this is likely not about the 64 TB limitation for software VSS providers, but note the limitations on this page, we might be hitting something similar here, but this is just a guess without a review of the logs.

But let's wait for the Support Team to update with their next steps, thanks!