On Sat, May 26, 2007 at 11:59:13PM +0200, Svein Halvor Halvorsen wrote:
> Roland Smith wrote:
> > You could use rsync instead of tar. That would save time.
> I'm not talking about saving time. But saving CPU time and HDD
> stress. However, the disk space issue is a bigger one:

rsync would do much less writing than tar. So it would save on "HDD
stress", whatever that is.

> >> (b) Undo all the bit flipping I have done, since I made the snapshot.
> > 
> > This is what the procedure above does if you replace the tar commands
> > with rsync.
> No, because the snapshot will still be in use, and hence all its
> bits will be kept intact and read-only. When I use rsync/tar/cpio or
> whatever to "undo" changes to a file system, I will in reality copy
> these bits to different places on the disk. And until I release the
> snapshot (which I very well could, since it would defunct after the
> restore process), I will use twice the amount of disk space.

You can't restore a previous situation _unless you saved it in some
form_. So if you want a possibility to restore stuff, you'll have to
keep a copy of it somewhere. Maybe in compressed form, and maybe you can
clump changes together in a smart way, but you have to save the bits
that you change.

Every revision control system (which is effectively what you ask for) uses
storage space to keep previous versions of data, although the precise
method used for this varies.

Disk space is cheap, and getting cheaper. Going through a lot of trouble
to save a few bytes is almost certainly not cost effective.

And keep in mind that you should really only use the tools that are
available in /rescue. Using a fancy port won't help you if whatever you
did borked /usr/local/bin. :)

R.F.Smith                                   http://www.xs4all.nl/~rsmith/
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