Question about subsequent backups, and about pruning

[UntouchedWagons]

Hi there, a quick question: Are subsequent backups incremental or differential?

Also, I don't quite understand how pruning works. In the example of attic prune /data/myrepo --keep-daily=7 --keep-weekly=4 shown on the project's website, how does attic know which 4 archives to keep?

[ThomasWaldmann]

answering your first question:

They are neither incremental nor differential, it's a different method. Every backup appears to be complete, but shares counted references to common chunks with other backups.

So you can remove anything you do not need any more without a problem.

[DavorSaric]

Sorry for bumping this but this means that when the first ever made backup which was created on server is full backup. If it is pruned due to defined retention policy, the second backup will hold al the data from the first one + differences? The second backup holds only dedup data and references to first one and because of the references that point to the first backup the files from the first backup will not be deleted but instead they will be marked as included in the second backup? Right? And that logic is the same for every next backup if I got it right.

[ThomasWaldmann]

@abbynormal, deduplicating backup programs’ approach is different from the older full/incremental (or differential) approach.

Each backup you create with attic (or borgbackup) is a full backup that references all data chunks it needs in a storage shared between all backup archives.

The space saving comes from identical chunks being only stored once in that storage (but can be referenced as often as needed).

So, don’t worry about deleting backups you do not need any more. The chunks used by other backups will be still kept in the storage and are only removed when they are not referenced any more.

[DavorSaric]

On 16.10.2015 17:20, TW wrote:

@abbynormal https://github.com/AbbyNormal, deduplicating backup
programs’ approach is different from the older full/incremental (or
differential) approach.

Each backup you create with attic (or borgbackup) is a full backup that
references all data chunks it needs in a storage shared between all
backup archives.

The space saving comes from identical chunks being only stored once in
that storage (but can be referenced as often as needed).

So, don’t worry about deleting backups you do not need any more. The
chunks used by other backups will be still kept in the storage and are
only removed when they are not referenced any more.

Thank you I got it. So basically a repo is a storage which holds all the
chunks and backups are just a point in time reference points to those
chunks. Right?

Btw. you said borgbackup. I have been using attic for a year and didn't
notice any problems. I see now that borg is a new fork with more
activity. Should I switch to borg?