Re: best backup strategy for full backup's
On Mon, Mar 10, 2025 at 11:09:38 -0000, Michael Niehren wrote:
Hi together,
actually i only do full-backup's of my virtual machines.
I use the for the backup the "old" strategy:
- virsh snapshot-create-as $vmname overlay --disk-only --atomic --no-metadata --quiesce
- copy the qcow2 image file
- virsh blockcommit $vmname $device --active --wait --pivot
- the guest agent in the VM got's an 2 seconds freeze/thaw intervall
Now i want to switch to the new strategy with "backup-begin".
- virsh backup-begin $vmname
- the guest agent does not got an freez/thaw signal
As the guest agent got's no signal, is the backup over "backup-begin" still
consistent ?
The backup api doesn't have integrated quiescing ...
Or do i have to be consistent to send an virsh domfsfreeze $vmname
before starting the backup and an
virsh domfsthaw $vmname it it is finished ?
... so if you want to use custom scripts and/or be sure that all caches
are synced then you need to do this manually.
The quiescing overcomplicates the recovery code paths if something fails
during the operation so for now we decided not to go that way for
backup.
If so, the time intervall between freeze/thaw would be on an huge
disk much more then 2 secords.
How come? The start of the backup job is supposed to be instant. Did you
observe any cases when 'virsh backup-begin' would take non-trivial time?
In fact what 'virsh snapshot-create' does when --quiesce is requested is
exactly the same as if you'd do it "manually".