[Borgbackup] Storage, CPU, RAM comparisons

[Bzzzz]

On Mon, 4 May 2020 20:10:44 +0100
Dmitry Astapov <dastapov at gmail.com> wrote:

In fact, at this time borg is only missing the possibility of doing
backups from several machines at once in the same repo and, may be,
relocate the clients' index files on the server.

Which raises two questions upon those two points :
* is it possible with the actual borg structure ?
* is it suitable ?

> So one difference which I already covered is that "storing deltas"
> requires you to store "base" to which you can apply this delta, and
> this has implications for backup removal.
>
> The second difference is that file names/paths are input for computing
> deltas, so if you move/rename files, this would generate large deltas,
> whereas borg will just see the same blocks all over again and "do
> nothing".
>
> A third difference is that you can easily find out which portion of
> backup is "unique" and which is "shared" -- with deltas, you only know
> the diff to the base.
>
> Speaking of diffs, borg could easily diff any two backups, which with
> deltas is not straightforward, unless you happen to have just a single
> base backup.
>
> If anything happens to your base backup and you detect it, you have no
> other choice that to take new base backup (and discard all the deltas
> you have to the corrupted base). With borg, if you detect corrupted
> blocks, your next backup will just store new copies of the block you
> lost at a fraction of the cost.
>
> With hardlinked rsync backups, the information about data blocks
> shared by different files is stored in the filesystem datastructures
> (inodes in case of ext4, etc). With borg, this information is kept in
> the data structure which is written into archive storage for every
> archive. For small files, this will require at least ~100B/file + some
> extra overhead for directories and such. For Linux kernel tree with
> ~60K files this would be on the order of 5-10 Mb (i think), which can
> easily add up in the context of the benchmark we are discussing....