Does guest-fsfreeze-freeze block writes?

[Amplificator]

Does running a backup as a snapshot in a VM (not container) lock the VM?

I can read on https://pve.proxmox.com/wiki/Backup_and_Restore#_backup_modes that running the backup in snapshot mode calls "guest-fsfreeze-freeze" - does that mean that the VM Is put into a sort of read-only state during the backup?

 

[TwiX]

Hi,
Yes but only the time needed for taking the snapshot. In fact no more than few seconds

 

[Amplificator]

So let's say I'm hosting several hundred websites in a VM - they will still be able to upload/delete/change data during the whole snapshotting operation (save for a second or two as you say)?

 

[TwiX]

From my understanding writes should go on a queue in RAM until FS becomes writable.

 

[Amplificator]

Great - it also makes sense.
It would be unfortunate if the entire VM was frozen for the entire duration that a backup takes. Let's say you back up terabytes of data, then it would be frozen for a little while. So it makes sense that it's only while the actual snapshot is "taken" that you might experience hiccups.