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Subject: Re: [PVE-User] Proxmox Backup Server (beta)
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On July 16, 2020 3:03 pm, Tom Weber wrote:
> Am Dienstag, den 14.07.2020, 17:52 +0200 schrieb Thomas Lamprecht:
>>=20
>> Proxmox Backup Server effectively does that too, but independent from
>> the
>> source storage. We always get the last backup index and only upload
>> the chunks
>> which changed. For running VMs dirty-bitmap is on to improve this
>> (avoids
>> reading of unchanged blocks) but it's only an optimization - the
>> backup is
>> incremental either way.
>=20
> So there is exactly one dirty-bitmap that get's nulled after a backup?
>=20
> I'm asking because I have Backup setups with 2 Backup Servers at
> different Locations, backing up (file-level, incremental) on odd days
> to server1 on even days to server2.=20
>=20
> Such a setup wouldn't work with the block level incremental backup and
> the dirty-bitmap for pve vms + pbs, right?
>=20
> Regards,
>   Tom

right now, this would not work since for each backup, the bitmap would=20
be invalidated since the last backup returned by the server does not=20
match the locally stored value. theoretically we could track multiple=20
backup storages, but bitmaps are not free and the handling would quickly=20
become unwieldy.

probably you are better off backing up to one server and syncing=20
that to your second one - you can define both as storage on the PVE side=20
and switch over the backup job targets if the primary one fails.

theoretically[1]

1.) backup to A
2.) sync A->B
3.) backup to B
4.) sync B->A
5.) repeat

works as well and keeps the bitmap valid, but you carefully need to=20
lock-step backup and sync jobs, so it's probably less robust than:

1.) backup to A
2.) sync A->B

where missing a sync is not ideal, but does not invalidate the bitmap.

note that your backup will still be incremental in any case w.r.t.=20
client <-> server traffic, the client just has to re-read all disks to=20
decide whether it has to upload those chunks or not if the bitmap is not=20
valid or does not exist.

1: theoretically, as you probably run into=20
https://bugzilla.proxmox.com/show_bug.cgi?id=3D2864 unless you do your=20
backups as 'backup@pam', which is not recommended ;)
=