Disable fs-freeze on snapshot backups

[drjaymz@]

2025 update for everyone getting this problem: the UI to disable the freeze-on-backup is already in stable.
You can find it inside VM -> Options -> QEMU Guest Agent -> Uncheck "Freeze/thaw guest filesystems on backup for consistency"
View attachment 87655
View attachment 87654

I have not seen a problem with guests that are at least kernel 3.2. Prior to that there looks like some kind of bug where the disk never recovers. It behaves exactly like the old days when you got the CHS wrong on a disk and you could read some things but others were corrupt or you got IO errors.
Its good to have the option to not freeze if that indeed the cause.

 

[VictorSTS]

2025 update for everyone getting this problem: the UI to disable the freeze-on-backup is already in stable.
You can find it inside VM -> Options -> QEMU Guest Agent -> Uncheck "Freeze/thaw guest filesystems on backup for consistency"

Just a note: that option is exposed in the webUI at least since March 2023 with the release of PVE7.4 (check release notes [1]):

[...]

• Running fsfreeze/fsthaw before starting a backup can now optionally be disabled in the QEMU guest agent options.

Note: Disabling this option can potentially lead to backups with inconsistent filesystems and should therefore only be disabled if you know what you are doing.

[...]

[1] https://pve.proxmox.com/wiki/Roadmap#Proxmox_VE_7.4

 

[isc30]

Maybe I'm doing something wrong but I'm having this problem with the latest versions of proxmox/qemu, for some reason when a VM is backing up (k3s node with longhorn) the longhorn filesystem crashes with "i/o readonly filesystem" error which takes down the whole cluster until the VM is rebooted after backup. I have tried many alternatives to get this working and the only thing that worked is marking the disk as no "IO Thread" + disabling fs freeze for the agent.