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.
>
> How big of a problem is this for you?
>
> Have you looked into the Virtual Backups, although I'm not sure this 
> would help you.

:)  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 case here it's rather a large issue (granted due to other 
problems like hardware or software issues that require restores of data 
and is NOT something that I want to continue, however we are living in 
an imperfect world) but to give you an idea the dataset size is about 
30-40TiB with restores anywhere from 2TiB to a full restore to back that 
back up again not only takes a LOT of tapes which is costly it also 
takes a LOT of time (day/weeks) where nothing else can be run.

What I have been doing which is just painful is do a full restore, then 
have to do a full backup right after then continue so a restore is 
actually the time of about 2x of a full.  (for a full set this is about 
9-10 days on LTO4).   This has happened about 3 times so far in the past 
2 months.



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