On Tue, Dec 07, 2010 at 07:58:05AM +0000, Tyler J. Wagner wrote:
> On Mon, 2010-12-06 at 10:51 -0800, Robin Lee Powell wrote:
> > IME it's *much* faster that way; you do BackupPC_TarPCCopy, and
> > then rsync the cpoll *without -H*. It shouldn't take any longer
> > than the actual data transfer time itself.
>
> So, if you wanted to copy the entire /var/lib/backuppc directory
> to another filesystem, what commands would you use, for example?
sudo -u backuppc /usr/share/backuppc/bin/BackupPC_tarPCCopy
/var/lib/backuppc/pc | ssh $host 'cat >/tmp/pc.tar'
rsync -aPv /var/lib/backuppc/cpool $host:/var/lib/backuppc/
ssh $host 'tar -C /var/lib/backuppc/ -xvf /tmp/pc.tar'
I have a script for this, in fact, for transferring single
/var/lib/backuppc/pc/[foo]/ directories between hosts. Going to
post it when it's a bit more tested.
> Why use BackupPC_TarPCCopy over just tar?
The backuppc pool is a bunch of files.
The pc directories are a bunch of *hard links* into the polo files.
There is no way to find out all the hard links to the same inode
except to check *each and every* file on the file system.
So if you use "rsync -H" or "tar -l", they have to generate a giant
table of the inode values of each and every file in both the
backuppc pool *and* the /var/lib/backuppc/pc/ dirs. On a decently
sized backup system this takes a long time, and a *LOT* of RAM.
BackupPC_tarPCCopy, OTOH, knows how backuppc's checksums are
generated. So it just walks all the /var/lib/backuppc/pc/ files,
generates a checksum, checks that that checksum is in the pool as
expected, and emits a tar hardlink line. You end up with a tar
that's just attrib files, hard link instructions, and logs, and you
end up with it *MUCH* faster than checking all possible inodes for a
match.
-Robin
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