[Borgbackup] use of borgbackup in fi-backup to save VM images

[Thorsten Schöning]

Guten Tag Chiarello Ernest,
am Dienstag, 7. September 2021 um 11:54 schrieben Sie:

> /Don't use the linux filesystem btrfs on the host for the image
> files. It will result in low IO performance. The kvm guest may even
> freeze when high IO traffic is done on the guest. /

Some of those tests/advices are old, so it might be worth it to test
on your own. While I prefer ZFS in general, things like freezing VMs
are often seen when hosts have a lot of free RAM for file system cache
available. I had exactly that with VBOX and ZFS in the past, because
the virtual controllers used for IDE/SATA etc. of VBOX were configured
to cache. For some use-cases this resulted in so many pending writes
in the cache, that the HDDs backing ZFS weren't able to catch up with.

Though, after disabling those caches things were fine again. And
Proxmox provides ways to disable those caches regardless of the
underlying file system as well, so things might simply not be as bad
as you quoted for BTRFS.

https://pve.proxmox.com/wiki/Performance_Tweaks#Disk_Cache

OTOH, as Proxmox seems to recommend ZFS anyway and supports that in
its own installers etc., I would simply use that instead of BTRFS.

> this is the reason why I use Urbackup <https://www.urbackup.org/>
> to back up data contained in VMs (files and databases).

Remember that only because you backup VM-contents that doesn't
guarantee any consistent individual file format state as well. Things
are most likely only SYNC-safe and hence crash consistent as well, you
need to make snapshots within the VMs in theory as well etc.

UrBackup might handle all of that for all supported OS or it might
not, better look twice. Especially as Linux lacks infrastructure like
VSS under Windows telling apps about snapshots beeing created, to make
their individual file formats consistent etc. It might be that
UrBackup only cares on Windows because VSS is available by default.

Mit freundlichen Grüßen

Thorsten Schöning

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