On Thu, Jan 27, 2011 at 11:15:59AM -0500, Phil Stracchino wrote:
> On 01/27/11 10:48, Graham Keeling wrote:
> > The same problems exist in more realistic situations.
> >
> > Assuming that I somehow know that all my backups will range from 100MB to
> > 10GB,
> > then what should I set?
> >
> > a) 10000 volumes, 100MB max size?
> > b) 100 volumes, 10GB max size?
> >
> > a) gives me wasted space when a backup is not a multiple of 100MB in size,
> > and possible overhead problems due to the number of volumes.
> > b) gives me wasted space when a backup is not a multiple of 10GB in size.
>
> If you insist on limiting your number of volumes to the number of
> maximum-size volumes that would fill your disk and restricting the
> number of jobs allowed on a volume, yes, one could argue that it does.
> But any time your Bacula pool design answer involves "Max Volume Jobs =
> 1", the probability is extremely high that you started out by asking the
> wrong question.
>
> The problem here is not that the directives don't work, or that any
> particular method of governing volume size wastes space. It's that ANY
> possible set of volume management options is capable of being misused to
> create pathological configurations that waste disk space. If you only
> allow yourself 100 volumes on a 1TB disk, and then write 1GB to each one
> and complain that the remaining 900GB of disk space is "wasted" because
> you can't create any more volumes and can't append to any of the ones
> you have, you only have yourself to blame; you consciously, with malice
> aforethought, took careful aim and shot yourself in the foot with an
> elephant gun.
Well done.
Now follow the thinking through. Luckily, I have already done that for you.
Remember, at the start you had three obvious options:
a) Make more volumes, reduce the max sizes.
b) Make more volumes, keep the max sizes the same.
c) Increase the number of jobs per volumes.
You have realised that (a) and (b) are not very good.
So you try (c) and increase the number of jobs per volumes.
Your suggestion was to use either 'Maximum Volume Jobs' or 'Volume Use
Duration'.
'Maximum Volume Jobs' initially appears to work because each volume can now get
filled up to its allocated size. But now, it becomes very difficult to work
out which volumes you are able to purge / recycle.
'Volume Use Duration' prevents the allocated space being used up, so it also
wastes space.
So, at this point, I am stuck.
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