Re: [BackupPC-devel] File growing 5x in backup copy compared to original.

[Dan P. <da...@in...>]

> On Wed, Apr 01, 2009 at 05:38:57PM +0000, John Rouillard wrote:
> > I am backing up a system using rsync and it has a (source) file that
> > is 40GB in size. Dring the backup it grows to 200GB in size.

your db file is probably a sparse file.  

rsync supports sparse files, but it's not part of the defaults.  Not sure
if backuppc's rsync module handles sparse; based on a quick look at the
args getting passed to the remote rsync, i don't think so.

If an application doesn't explicitly know to look for sparse files it
will get a null-padded file when it reads the file.  It'll take forever
to read over the network and will fill the disk on the backup server if it
gets written before compression (which i think it does).  Obviously it will
compress very well if you can ever actually do the compression.

if backuppc doesn't do sparse, as a workaround you can run a job on the
backup client to make a compressed local copy of the file, and back that
up instead.  

with moderate-sized sparse files it's just a little overhead but in your
case it is clearly a big problem :)

danno