Re: replicating backup servers offsite

Rich Duzenbury writes:

> I use LVM and snapshot the drive.  Then I use dd_rescue to copy it to a
> removable hard drive in the same machine.  This copies the entire
> partition, empty blocks and all, but I copy about 80Gb in 90 minutes.
> 'cp -a' takes many hours.   Of course this doesn't help much, because
> it's not in a remote location.
> 
> I've seen reference to this trick, but never tried it:
> tar cf - / | ssh -C host 'cd /mnt; tar -xf -'
> I would think you would have to stop backuppc and unmount the drive for
> this to be safe.
> 
> For a 'live' backup to a remote device, I've been considering the
> 'Enhanced Network Block Device'.  Again, haven't yet tried it.
> http://www.it.uc3m.es/ptb/enbd/
> Also, I don't know that it supports any kind of encryption.

I wonder whether you can use rsync's --inplace option to
directly sync two raw devices, eg: localhost /dev/hda1
and remote:/dev/hda1?  You would needs rsync's block size
to be a multiple of the disk's block size.  I would guess
the geometry needs to be the same.  Plus, by default,
rsync tries to match blocks on any byte boundary, which
is not desirable since you would only want to match on
block boundaries.

Actually, rsync by default doesn't open any non-regular
files, so this would not work.  But with a few changes
to rsync you should be able to do efficient incremental
updates of raw disk devices.

Perhaps this is a good topic to post on the rsync list?

Craig


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