Re: [rdiff-backup-users] independantly writing to the mirror

[Ben Escoto]

On Fri, 14 Nov 2003 15:27:17 +0000 Toby Dickenson <address@hidden> wrote:
> I am hoping to use rdiff-backup in a scenario where I might make
> independant changes to the mirror.
> 
> I intend to use it to maintain a complete remote operating system
> backup. Occasionally I might boot that backup for some other
> purpose, and may make some changes. I hoped that I could then re-run
> rdiff-backup to erase those changes, restoring the backup to a clean
> copy of the source filesystem. (The man page warns that I might be
> unable to access old revisions after doing that, which I can live
> with.)
> 
> Unfortunately I am seeing that it does not always resync all files
> that were changed on the mirror, I guess because the change is not
> recorded in the metadata cache. Is there a way to force it to fully
> check the mirror filesystem? Will that do what I want, or is there
> some other danger?

rdiff-backup recovers old files by applying a string of diffs:

Current -> diff1 -> diff2 -> ... etc

so if you make changes to current you can break the chain and lose
your old revisions.  This is true on a file-by-file basis, so if you
only change certain files in theory you only lose the history of those
files.

But rdiff-backup doesn't have any functionality to keep track of a
partially corrupted archive.  It would be cleanest from rdiff-backup's
point of view if, after you boot the backup, you "rm -rf
.../rdiff-backup-data" and then run the next session with --force.
This will explicitly erase all history.

If you wanted to keep only some of the history, you could try removing
the metadata cache file ("rm
.../rdiff-backup-data/mirror_metadata.<most recent time>.snapshot.gz")
which should cause rdiff-backup to read the metadata directly from the
file system.  However, rdiff-backup requires a metadata file to
regress, so if your next backup fails, you will have to manually
remove some files (see
http://rdiff-backup.stanford.edu/FAQ.html#regress_failure) before it
works again.


-- 
Ben Escoto

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