rsync and moving files [Re: backup w/ snapshots]
freebsd at meijome.net
Mon Aug 29 16:14:55 GMT 2005
Svein Halvor Halvorsen wrote:
> * Norberto Meijome [2005-08-30 00:32 +1000]
>> isn't that the whole point of having a backup? to have *another* copy of your
> Well, yes and no.
> The idea is that I have a main computer that I want to backup. I want the
> backup to be (a) remote, (b) incremental and (c) random-accessible.
> So I thought that every day my backup-server could rsync my main computer,
> creating a mirror of the relevant directory trees. Then, as soon as the
> rsync job completes, it takes a snapshot of the filesystem. This snapshot
> could be mounted r/o and nfs-exported back to the original computer.
yes, that sounds like it would meet your criteria.
> Now: If I have a file /foo/test on my main computer. After the first
> rsync-job this file will be copied, assigned an inode and put on the disk
> somewhere. If I change this file, a local snapshot will be smart enough to
> just store the changed sectors that this file now occupies.
I take your word wrt to how it works. Assuming of course that you move
within the same filesystem.
> But: If I move the file from /foo/test to /bar/test on my main computer,
( /foo/ and /bar/ being in the same filesystem)
> rsync will create a BRAND NEW FILE in /bar (and delete the file in /foo,
> since I used the --delete option). Now this NEW file will have a new
> inode, and cover new sectors on disk. The snapshot will then tak
> considerable more diskspace. If I move a large directory tree this way,
> this will occupy huge amounts of diskspace.
(touche). yup, that's what would happen....but tha's the nature of the
beast :) don't keep too many snapshots ? ;)
it'd be great if you could keep a log of all local-mv operations,and
then replay them remotely via ssh.
<hack> replace mv with your own version which does local-mv and either
does remote-mv over ssh or sends a msg to a service to perform the
transaction</hack> (yes, there may be other conditions that trigger the
same effect as an mv...I just dont know which ones)
I guess the proper way to do this (if you are REALLY REALLY worried
about that extra spaced used for snapshots in the remote site) would be
to implement a GEOM class that knows about the remote site and the 'mv'
condition and communicate to the remote end.
> So how can I make rsync know that the files were just moved (renamed,
> relinked), and make rsync reflect this fact on the remote mirror?
rsync would then be the wrong tool for the job.
I would suggest that you just get more or larger drives for the remote
site and live with the waste :) (though the GEOM class would be cool :D )
hmm...what about network operating systems like AFS or CODA (not that I
know much about them, I just read some stuff on those being distruted,etc..)
Let us know how you solve this.
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