VM frozen after backup

[Matwolf]

Hello,
I have a backup job running every day backing up my VMs using snapshot mode.
Everything is running ok but sometimes one specific VM freezes (I have 4 VMs running but it happens only with one of them).
At the exact time of the backup the VM stop responding (even from the console) and I can see constant 50% CPU usage on the summary graph.
The backup terminates succesfully but the VM is marked as running, but actually completely frozen. Console shows the login prompt, but no keyboard input is processed. I can only reset it (reboot or shutdown don't work).
The VM is running Ubuntu server 22.04.
I'm running PVE v. 8.4.1.
Any Ideas?
Thanks in advance

 

[fiona]

Hi,
make sure you are using IO Thread for the VM disks and if you are using a network storage as the backup target, it might help to enable fleecing: https://pve.proxmox.com/pve-docs/chapter-vzdump.html#_vm_backup_fleecing

Please share the system logs/journal from around the time the issue happened, the backup task log and the output of the following:

pveversion -v
qm config <ID>

replacing <ID> with the actual ID of the VM.

You could also install the following packages apt install pve-qemu-kvm-dbgsym gdb systemd-coredump libproxmox-backup-qemu0-dbgsym and the next time a VM gets stuck, run:

qm status <ID> --verbose
gdb --batch --ex 't a a bt' -p $(cat /var/run/qemu-server/<ID>.pid)

again replacing with the actual ID both times.