[PVE-User] pbs incremental backups

[Arjen]

On Tuesday, March 2nd, 2021 at 11:22, mj <lists at merit.unu.edu> wrote:

> Hi,
> 

> Testing PBS backups taken from PVE VMs on ceph rbd now. Very nice, very
> 

> quick, very cool. :-)
> 

> We have a question. Something we wonder about.
> 

> In our current backup software, we make weekly full_system backups, and
> 

> daily incremental_system backups, each incremental based on the same
> 

> full_system backup. So: each daily incremental backup becomes bigger,
> 

> until the weekend. Then we make a new full_system backup to base the
> 

> next set of incrementals on.
> 

> In PBS I cannot specify if a backup is full or incremental, we assume
> 

> this means that automatically the first backup is a full_system backup,
> 

> and subsequent backups are incremental. The PBS backup logs confirm this
> 

> assumption, saying: "scsi0: dirty-bitmap status: created new" vs "scsi0:
> 

> dirty-bitmap status: OK (7.3 GiB of 501.0 GiB dirty)"
> 

> And now the question: At what point in time is a new full_system backup
> 

> created, to rebase incremental backups on?
> 

> Or is each incremental backup based on the previous incremental? And if
> 

> that is the case, how will we ever be able to delete one of the
> 

> in-between incrementals, because that would then break to whole chain of
> 

> incremental_backup-based-on-incremental_backup...?
> 

> We have read the page
> 

> https://qemu.readthedocs.io/en/latest/interop/bitmaps.html but it does
> 

> not seem to answer this.
> 

> Anyone care to share some insight on this logic and how PBS works?
> 

> MJ

Accoring to the documentation every backup is a full backup and the data is deduplicated.
There are no incrementals and the dirty-bitmap is just a optimization.
See https://pbs.proxmox.com/docs/faq.html#is-the-backup-incremental-deduplicated
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