Re: [BackupPC-users] Matching files against the pool remotely.

On Fri, 18 Dec 2009, Malik Recoing. wrote:

> The Holy Doc says ( Barratt:Desing:operation:2 ): "it checks each file in the
> backup to see if it is identical to an existing file from any previous backup 
> of
> any PC. It does this without needed to write the file to disk."
>
> But it doesn't say "without the need to upload the file in memory".
>
> I know a file will be skiped if it is present in the previous backup, but what
> appens if the file have been backed up for another host ?

It is required to be uploaded first as otherwise there's nothing to
compare it to (yeah, I know, that's a pain[1]).

It might theoretically be sufficient to let the remote side calculate a
hash and compare it against the files in the pool with matching hashes,
and then let rsync do full compares against all the matching hashes in the
pool (since hash collisions happen), but I don't believe anyone has tried
to code this up yet, and it would only be of limited uses in systems that
were network bandwidth constrained rather than disk bandwidth constrained.

[1] I just worked around this myself by copying a large set of files onto
sneakernet (my USB key), copying them onto a directory on the local backup
server, backing that directory up, then moving the corresponding directory
in the backup tree into the previous backup of the remote system, so it
will be picked up and compared against the same files when that remote
system is next backed up.  I find out tomorrow whether that actually
worked :)


-- 
TimC
            Computer screens simply ooze buckets of yang.
    To balance this, place some women around the corners of the room.
                                        -- Kaz Cooke, Dumb Feng Shui

------------------------------------------------------------------------------
This SF.Net email is sponsored by the Verizon Developer Community
Take advantage of Verizon's best-in-class app development support
A streamlined, 14 day to market process makes app distribution fast and easy
Join now and get one step closer to millions of Verizon customers
http://p.sf.net/sfu/verizon-dev2dev 
_______________________________________________
BackupPC-users mailing list
BackupPC-users AT lists.sourceforge DOT net
List:    https://lists.sourceforge.net/lists/listinfo/backuppc-users
Wiki:    http://backuppc.wiki.sourceforge.net
Project: http://backuppc.sourceforge.net/