Title: Slow Backup Performance with Commvault Agentless Backup on XCP-ng Cluster

yeopil21

Hello,

We are currently experiencing very slow backup speeds when using Commvault's agentless VM backup in the following environment:

Environment:
Commvault Server - Windows server 2019
Hypervisor: 3-node XCP-ng cluster
Shared Storage: NetApp iSCSI SR
Backup Solution: Commvault (v11.36.49)
Backup Method: Agentless VM backup
Backup Target Storage: NetApp NFS volume

Issue:
When backing up virtual machines via agentless mode, the transfer speed is extremely slow—just a few MB per second—resulting in backup jobs taking several hours to complete.

No significant load on the VMs being backed up
No bottlenecks observed in Commvault job logs
All basic network(1Gbps) and disk performance checks look normal

Questions:
Are there any known limitations or bottlenecks for Commvault agentless backups on XCP-ng environments?
Which parts of the backup flow (e.g., VM snapshot, disk read, CBT parsing) typically cause performance issues in agentless mode?
Any recommended best practices or settings to improve agentless VM backup speeds in this setup?

olivierlambert

Hi,

I think the best first approach is to ask Commvault. It might be interesting to compare with XO to check if it's the same ballpark numbers for backup speed.

yeopil21

We are currently experiencing very slow backup speeds when using Commvault's agentless VM backup in the following environment:

Environment:
Commvault Server - Windows server 2019
Hypervisor: 3-node XCP-ng cluster
Shared Storage: NetApp iSCSI SR
Backup Solution: Commvault (v11.36.49)
Backup Method: Agentless VM backup
Backup Target Storage: NetApp NFS volume

Issue: VM Backup – Unmount Process Taking 10+ Minutes Is This Normal?
We're currently running backups for several VMs in our XCP-ng environment using Commvault(3rd-party backup solution)
During the backup process, we’ve noticed that the unmount step consistently takes around 10 minutes to complete for certain VMs.

Questions:

Is this a normal behavior during the backup process?
Are there any known causes (e.g., high I/O, slow SR response, snapshot handling issues) that could lead to this delay?
Any recommendations to reduce this time?
Has anyone else experienced long unmount durations like this?

There are no obvious errors in the logs, and backups do complete successfully – just very slowly at the unmount stage.
Any insight would be greatly appreciated.

olivierlambert

Before answering your question, that would be good to get already something to compare. Can you try with XO and see if it's similar? It's important to understand, if the problem is related to XCP-ng or your backup solution. Also, why not asking CommVault directly too?