Steve Costaras schrieb:
> 
> 
> Some history:
> 
> On 01/14/2010 16:24, Dan Langille wrote:
> > Steve Costaras wrote:
> >> On 01/14/2010 15:59, Dan Langille wrote:
> >>> Steve Costaras wrote:
> >>>> I see the mtimeonly flag in the fileset options but there are many
> >>>> caveats about using it as you will miss other files that may have been
> >>>> copied over that have retained mtimes from before the last backup.
> >>>> Since bacula does an MD5/SHA1 hash of all files I assumed (wrongly it
> >>>> seems) that it would be smart enough to not back up files that it
> >>>> already had backed up and are on tape.
> >>> Smart enough?  Sheesh.  ;)
> >>>
> >>> That hash is to ensure the file is restored properly.  And for 
> >>> verfication.  To do what you want is not easy.
> >> :)  Well I figured it would be relatively easy as an option (since 
> >> the hash is in the database and when a file is read from disk for 
> >> backup (since it's planning on backing it up anyway it would need to 
> >> read the file, if the file name & hash match those that are in the 
> >> database the file could be skipped.   (for 'real' completeness and to 
> >> keep in line w/ the accurate option perhaps update the database with 
> >> permissions et al on the inode but since the content matches that 
> >> would save a lot of tapes).
> >
> > In the database... not on the client.  That's the issue.  Let us not 
> > discuss this here.  It is not a trivial problem to do correctly.
> 
> I see your point, the fd would need to get this data (or send the hash 
> of the file to the director) 1) after reading and calculating the entire 
> file and 2) before sending it to the director to save not only time but 
> network bandwidth, not to mention 3) having need to buffer the file data 
> in memory or to do another file system look up and re-read of the same 
> data which if done could cause more of a window for a race condition 
> unless handled properly if the file was modified between the two reads 
> and when the data was stored in the catalogue.
> 
> That would be assuming you wanted to save both network bandwith and 
> tape.   Otherwise if the fd acted normally and the decision was made by 
> the director?  Does the FD talk directly to the SD or does it need to go 
> through the director as well?

You might want to look into the new Accurate Backup feature.

http://www.bacula.org/manuals/en/concepts/concepts/New_Features.html#SECTION00310000000000000000

But I think it won't help you here. What be more interesting,
especially with your amount of data is the upcoming Base Job feature.

http://sourceforge.net/apps/wordpress/bacula/2009/09/30/new-basejob-feature/

Ralf

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