<hansbkk <at> gmail.com> writes:

> 
> Or even (forgive me please rabid BackupPC devotees) consider another
> tool to handle those special-case files.

I've done a bit of investigation on this.  I used rdiff, which is a command-line
interface to the algorithm used by both rsync and rdiff-backup.  It looks like
this particular database backup is mostly the same, but updates -- block
timestamps perhaps? -- are scattered throughout.  rdiff delta ran extremely
slow, and after having processed about 10% of the file, had generated a 400MB
delta already, so probably would have wound up with a 4GB delta against the 20GB
file.  I don't know if rsync has particularly slow performance against
block-type files where blocks remain similar but each block header changes, but
that may be what's happening here.

A 4GB .bz2 representation of this same data didn't have this problem, so I am
going to test gzipping the file on the server and transferring that.

> rdiff-backup  is designed  for exactly this type of scenario - very
> large files that only change a little bit from one run to the next -

I have used rdiff-backup myself for a number of years but for various reasons
(chiefly performance) I don't think it's suitable for me here -- but thanks for
the tip.

-- John



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