On Thu, Jan 27, 2011 at 06:26:04AM -0500, Phil Stracchino wrote:
> On 01/27/11 06:12, Graham Keeling wrote:
> > Perhaps 10GB becomes more reasonable if you allow more than one job per 
> > volume,
> > but then you still have the problem of disk space being wasted because you
> > cannot purge the volume until the last small 1MB job passes its retention 
> > time.
> > 
> > I think this last problem is what Phil is trying to solve by setting either
> > Maximum Volume Jobs or Volume Use Duration. But these solutions seem
> > unsatisfactory for disks (I can't comment on tapes because I don't know 
> > enough
> > about them).
> > You are wasting space if the volume is not full up by the time Volume Use
> > Duration expires.
> 
> Define "full".  Disk volumes aren't like packing crates.  They're more
> like balloons.  They grow as you add data to them.
> 
> > And you are wasting space if the volume is not full up with Maximum Volume
> > Jobs.
> 
> Again, how is it "wasting space"?  A disk volume doesn't preallocate
> space to hold the maximum size of the number of jobs you might write
> into it.  A disk volume consumes only as much space as the data you
> wrote into it.

The idea is to split the disk up into equal-sized chunks. 
In this scenario, you have specified a number of volumes, and a maximum size
for each volume. For example, on a terabyte disk, you might define 100 volumes,
10GB each.

If you don't use the "full" 10GB in each volume, the space that you don't use
is wasted.

You can't use the unused space for some other application, because the volume
might get purged, recycled, and then the next job that writes to it wants to
use all 10GB - you will then find that it can't.

You can't just add more equal-sized volumes, because then you'll have more
potential for running out of space. The maximum space that your
volumes can balloon to will be bigger than your disk.


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