On Wed, Mar 6, 2013 at 9:28 AM, Maarten <mtp AT milieudefensie DOT nl> wrote:
>
>>> So my question is: can anybody think of an elegant way to re-use the
>>> > currently backed up data so that I can keep the current backups and not
>>> > start from scratch? The not-so-elegant solution that comes to mind is to
>>> > rename the old host on the BackupPC server and create symlinks so that
>>> > the old directories still exist on the new server.
>>
>> I think you've missed the main point of backuppc which is that it
>> pools all files with identical content regardless of where it finds
>> them.   Assuming you are storing the archive on a single filesystem
>> with the pool hardlinks working correctly, the old files in their new
>> location will be copied over once, then replaced with hardlinks to the
>> existing pooled copy.   After that you'll have a new directory tree
>> for rsync to use for subsequent runs.
>
> Thanks for the quick response. I assumed that BackupPC was just creating
> hardlinks in the pool for files on the same location. If what you say is
> correct, does that mean it calculates checksums of each file, hence
> never saving a duplicate file no matter where it resides on the filesystem?
>
> That would be perfect.


Yes - the pool/cpool directory is full of extra hardlinks where the
hash of the content is the name to quickly match up new items (plus a
little extra work to deal with collisions).  Rsync just follows the
existing pc directory tree though, so you do have to copy the data
from each new location once, but storage is all pooled.  If the target
system is local, that usually isn't a problem.  If it is over a
low-bandwidth connection it might be worth some extra work to fake the
initial tree with a copy of the old link tree.

-- 
   Les Mikesell
     lesmikesell AT gmail DOT com

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