On Sat, 7 Mar 2009 08:04:17 -0800
Grant <emailgrant@gmail.com> wrote:

> I'm backing up numerous large files on another machine on my local
> network.  I've only been using rsync, but it occured to me that I
> might be able to save some time and space if I incorporate tar and
> bzip2.  How will rsync interact with those?  If I turn the whole
> backup into a big tar.bz2, would rsync need to redownload the whole
> thing if I change one file?  If so, maybe I should turn different
> groups of files into tar.bz2 archives so rsync only needs to
> redownload an archive if one of its files has changed?

It's not a default behavior, but there is an '--inplace' option.

Also,there is a '--compress' option, if the bandwith is the only
problem, otherwise you can use lzma (with normal-best ratio) to either
acheive much better compression than bzip2 or still slightly better
ratio with improved speed / less cpu time with 'lzma -1' (fast mode).

And if you're going to put a lot of files (like whole fs) into a
single tar just to transfer it to some remote destination, prehaps you
shouldn't be using rsync at all, since you'll end up reading all the
files anyway to create the tar.
Alternatively, you can save disk space on the source machine by piping
tar directly to destination, with compression either on the source to
lessen the banwidth, or on the remote to lessen the load on the source
machine cpu.

That said, you can also use tar to create (or pipe) incremental backups
- just the changes since the time last one was made. Tar can handle that
as easily as rsync does, since it checks what needs to be transferred
each time anyway.

-- 
Mike Kazantsev // fraggod.net