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Re: [Bacula-devel] Optimizing disk based backups


On Friday 23 May 2008 20:53:13 Adam Thornton wrote:
> On May 23, 2008, at 1:31 PM, Michael Short wrote:
> > Hello,
> >
> > I realize that Bacula was originally developed for tape based backup
> > systems, but disk space is becoming more inexpensive everyday. It is
> > cheaper and more reliable to maintain a system which uses disk based
> > mediums to store backup data. The problem is that disk based restores
> > are unnecessarily slow, due to the linear nature of the backup
> > volumes.
> >
> > I am addressing this problem because at some point it would be
> > necessary to access old backup archives should anyone implement an
> > rsync or xdelta type enhancement for Bacula. Perhaps instead of
> > storing individual file locations in the catalog, an index of the
> > backup could be stored at the beginning or end of a volume, so that
> > unnecessary "forward spacing" would no longer be needed for disk based
> > volumes. This extra would also make the process of recovering catalog
> > information from volumes much less painful.
>
> Well, if you put the index at the front of the volume, then you break
> tape volumes.
>
> I would suggest that the right way to do this is to, if you're backing
> up to disk volumes, have many more volumes each of which is much
> smaller.
>
> Set your maximum file size to be, say, 1GB (or 100MB or whatever your
> own personal tolerance is), and then have Max Volumes be very large.
> Locating the right volume is therefore a matter of a SQL lookup and
> locating the file within it is a much smaller seek problem.

With older Bacula the above is true, but with later versions, restoring from 
volumes of any size is equally rapid.  Of course, if you ever want to copy 
your volumes or for other reasons, you might want to limit their size, but 
even a 50GB Volume should pose no problems in terms of performance as 
compared to a volume of 1GB -- in fact the restore might be faster since if 
the restore is spread over more Volumes Bacula has to do a bit (very small) 
of extra work (opening and closing volumes).


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