The way to do it on linux is to use network block devices and to a raid1 mirror on the primary backuppc volume with the second volume being the nbd that actually writes to a drive on another server.  Then during normal operation when nbd is detached and missing from the raid, and nightly you attach it and the normal linux raid code will mirror the drive.

This works live without getting in the way of backuppc's operation and it relatively fast.

There are lots of howto's on this subject and whole companies formed around solutions in this area, but for what you want most of those solutions are more than you need.

The net result is an online copy of the whole filesystem and you bypass the issue of hardlinks completely.
And if the network is fast it is way faster than the time it takes rsync to process all that data.

-Wayne

On Wed, Jun 3, 2009 at 2:24 AM, Alex Harrington <alex@longhill.org.uk> wrote:
Hi Filipe

> I just bought some big disks to a spare server I have, I plan
> to create a local RAID5 volume to use as the BackupPC main
> repository and leave BackupPC working there on the local
> disks. To do my off-sites, I plan to use rsync -aH to
> duplicate that data into the external USB disks. If I need to

I think you'll find that that won't work. Whenever I've tried to copy a
relatively small backuppc install, the number of hardlinks cause tools
like rsync to run out of RAM and fail.

I've yet to see a good way of doing that for multi-terabyte pools
documented - and at present we basically image the whole drive that
backuppc is on and offsite that, but it's slow and a manual process.

Cheers

Alex

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