[PVE-User] pbs incremental backups

mj lists at merit.unu.edu
Tue Mar 2 11:22:55 CET 2021


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




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