Re: [Bacula-users] Bat: wrong Vol Usage in Media pane

On 08/25/10 07:05, Niccolo Rigacci wrote:
> I'm using a pool of LTO-4 tapes, each one should contain about 
> 800 Gb.
> 
> Bat reports a totally wrong Vol Usage: a tape with 531 Gb is 
> reported full at 692%!
> 
> Reading the sources, it seems to me that Bat estimates the size 
> of the media computing the average size of all the full or used 
> volumes of the same type.
> 
> But if the medias are rotated before they went full, the estimate 
> is totally wrong!
> 
> In the database I see a maxvolbytes field for each media (set to 
> zero), may be Bat can use that value (if different from 0) to 
> compute the Vol Usage.

The maxvolbytes field is intended for disk volumes where you want to
control the maximum size of the volume on disk, particularly if you
intend to copy the resulting volumes off to DVD.  It's difficult to
produce a useful maximum volume size for tape volumes because with
hardware compression enabled on the drive, you don't know in advance how
much data is actually going to fit on the tape.

You're correct that the percentage volume usage is not necessarily that
useful in the case of tape media.  I suppose about the only way around
this would be to add an optional "Expected Capacity" field, that would
default to MaxVolBytes if MaxVolBytes is not zero, but otherwise would
be defined by the user.


-- 
  Phil Stracchino, CDK#2     DoD#299792458     ICBM: 43.5607, -71.355
  alaric AT caerllewys DOT net   alaric AT metrocast DOT net   phil AT 
co.ordinate DOT org
         Renaissance Man, Unix ronin, Perl hacker, Free Stater
                 It's not the years, it's the mileage.

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