Re: [PVE-User] Proxmox Backup Server (beta)

["Fabian Grünbichler" <f.gruenbichler@proxmox.com>]

On July 16, 2020 3:03 pm, Tom Weber wrote:
> Am Dienstag, den 14.07.2020, 17:52 +0200 schrieb Thomas Lamprecht:
>> 
>> 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.
> 
> So there is exactly one dirty-bitmap that get's nulled after a backup?
> 
> 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. 
> 
> Such a setup wouldn't work with the block level incremental backup and
> the dirty-bitmap for pve vms + pbs, right?
> 
> Regards,
>   Tom

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

probably you are better off backing up to one server and syncing 
that to your second one - you can define both as storage on the PVE side 
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 
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. 
client <-> server traffic, the client just has to re-read all disks to 
decide whether it has to upload those chunks or not if the bitmap is not 
valid or does not exist.

1: theoretically, as you probably run into 
https://bugzilla.proxmox.com/show_bug.cgi?id=2864 unless you do your 
backups as 'backup@pam', which is not recommended ;)