On Mon, 4 Nov 2002 at 6:33pm, Galen Johnson wrote

> After further study of the restore issues I've had with amanda (mostly 
> tar related) I have just today run into what I feel is another problem 
> (I suspect is a combination of tar and amanda in this case).  I am 
> concerned with the "incremental" backups.  Amanda seems to treat 
> incrementals as differentials in the way it labels them for later 
> recovery when used in conjunction with tar (I have no idea how it works 
> with dump).
> 
> The way I understand incrementals is that and incremental is just the 
> files changed since the last incremental or full.  A differential is the 
> files changed since the last full backup (from what I've seen this is 
> how amanda treats the "incremental" whereby it only increments the 
> "level" by 1 if it meets certain criteria (which I'm fairly certain are 
> definable in amanda.conf)).

Amanda with tar works just as with dump, including with regards to 
incrementals.  An incremental is anything less than a full, a.k.a. a level 
0.  There are multiple levels of incrementals.  Any level backs up 
everything that has changed since the last backup of a lower level.  I.e. 
a level 1 backs up everything changed since the last level 0.  A level 2 
backs up everything changed since the last level 1.  Etc etc etc.

> I hope I've made clear what I'm trying to point out.  The "incremental" 
> as amanda deals with it is really being treated as a differential in 
> regards to a restore.  Can anyone recommend any suggestions to make this 
> behavior a bit more along the  accepted norms?  I was thinking of 
> setting the default amanda.conf bumpsize of 20 Mb to 1 Kb to see if it 
> will set the incrementals to give truer incrementals.
> 
> Any thoughts on this matter are greatly appreciated.

Well, you could do that, and get higher levels, but why would you want to?  
If all your incrementals are level 1s, then you'll only ever need two 
tapes to do a full restore -- the last level 0, and the latest level 1.  
The more levels of incrementals you use, the more tapes you'll need to 
restore from.  If you've got the tape space, why not use it?

In short, it's a feature meant to save you time at restore time and 
protect you against the possibility of bad tapes.

-- 
Joshua Baker-LePain
Department of Biomedical Engineering
Duke University