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

[devzero at web.de]

> Though, after disabling those caches things were fine again. 

*sigh*

there are longstanding bugticket regarding freezing, see  https://bugzilla.proxmox.com/show_bug.cgi?id=1453 and https://bugzilla.kernel.org/show_bug.cgi?id=199727 for example

think it needs some kvm & zfs expert to get this resolved... 

at least proxmox team is willing to investigate into this. apparently, kvm folks completely ignore bug #199727 since 2018...

regards
roland


> Gesendet: Dienstag, 07. September 2021 um 12:47 Uhr
> Von: "Thorsten Schöning" <tschoening at am-soft.de>
> An: Borgbackup at python.org
> Betreff: Re: [Borgbackup] use of borgbackup in fi-backup to save VM images
>
> 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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