Re: [rdiff-backup-users] How much extra space should there be on a target file system?

[Mike Fleetwood]

On Sun, 1 Sep 2019 at 19:39, Theodore Wynnychenko <address@hidden> wrote:

> Hello
>
> I have been searching for an answer or guidance to this question, but have
> not been able to find anything, so I will ask here.
>
> I am sorry if it has been asked/answered before.
>
> In any case, I am planning on "updating" my backup hardware, and will
> probably switch from rsync to rdiff (I have used rsync for many years, and
> have been happy with it, except for that one time years ago when I deleted
> a
> bunch of files and did not notice until about a day later, and 10 minutes
> after the final backup had been synced - a bit disappointing).
>
> Anyway, I am wondering if there is any guidance on how much larger the
> target file system should be compared with the source file system when
> using
> rdiff?
>
> Clearly, rdiff stores more information, so, in theory, if you have two file
> systems of exactly the same size, and the source is completely full, then
> rdiff would have nowhere to store any historical changes.
>
> Is there a rule-of-thumb, or some sort of calculation that will give
> guidance on how much extra space there needs to be on the target file
> system
> to reliably not have an instance when the target file system becomes full,
> while the source still has space on it?
>
> It seems this would be based on the frequency of updates, the size of the
> file system, the number and size of files, the types of changes made to
> those files, how long backups are maintained, and probably other things.
>
> I am not looking for anything exact, more just a way to guesstimate.  But,
> I
> am also not opposed to math either, if there is a calculation that can help
> determine the target file system's appropriate size.
>
> Thanks
> Ted
>

Just a user here who backups up their home Linux desktop using
rdiff-backup.

So it all depends on your rate of change of backed up data and how long
you want to keep previous backups for.

As an example here are some figures from my daily backup:

    Backup                   Size    Pct
    --------------       --------    ----
    Current mirror       42.8 GiB    100%
    Day 406 increment    65.4 GiB    150%
    Day 804 increment    87.2 GiB    200%

So for *MY* data and *MY* rate of change, 150% is enough for over a year
of daily backups.  Make sure your backup file system has enough inodes
as well as free space.

Mike