VMs are not responding during backups

[SamoPM]

During the period of backups, VMs have problems with connectivity.
They are not responding during the backup is taking place. Backups are succesfull.

Env: PM 9.0.6

 

[Daniel-Doggy]

Do you have the guest agent installed and running on the VM?
And have you enabled the guest agent option in the VM options?

If not then that is why.
If the guest agent is not running or enabled then it will freaze the VM and not unfreaze it.
The agent is needed to create a consistant state while still allowing the VM to be unfrozen during the backup.

 

[SamoPM]

@Daniel-Doggy

Thank you for the response. We don't have the guest agent installed and we will look into it.

But we hadn't have these types of issues before switching the backup storage. After noticing this issues, we switched back. But the problem remains.


Do you by any chance have any other ideas, what could be casuing this issue.

 

[Daniel-Doggy]

Hmmm…

Looking at the docs. (https://pve.proxmox.com/wiki/VM_Backup_Consistency) it seems that guest agent is not required as I thought. (But really incurraged.)
My next troubleshoot step would be to create a new VM and try to do the same thing. (To see if it is a issue with the VM itself or something else.)

 

[PwrBank]

Some one correct me if I'm wrong, but I believe this is the issue... When you are creating a backup while the VM is running all writes will go to the backup storage, so if the backup storage is slow, the VM will effectively freeze up. A way to test this would be to enable Fleecing on the backup job and see if that eleviates the issue.

Source: https://pve.proxmox.com/pve-docs/chapter-vzdump.html#VM Backup Fleecing

When a backup for a VM is started, QEMU will install a "copy-before-write" filter in its block layer. This filter ensures that upon new guest writes, old data still needed for the backup is sent to the backup target first. The guest write blocks until this operation is finished so guest IO to not-yet-backed-up sectors will be limited by the speed of the backup target.
With backup fleecing, such old data is cached in a fleecing image rather than sent directly to the backup target. This can help guest IO performance and even prevent hangs in certain scenarios, at the cost of requiring more storage space.