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Re: [Bacula-devel] Multiple storage daemons - multiple scratch pools?


Le Thursday 11 December 2008 14:17:09 Robin O'Leary, vous avez écrit :
> On Thu, Dec 11, 2008 at 01:29:48PM +0100, Eric Bollengier wrote:
> > Le Thursday 11 December 2008 12:34:42 Graham Keeling, vous avez écrit :
> > > Since sending my original patch, we came up with a slightly different
> > > idea that required much less change to the code, and is therefore
> > > likely to be safer. I am currently using this new idea instead of the
> > > original one.
> > >
> > > It goes like this:
> > > If Pool A needs a volume and has a RecyclePoolId is pointing to a Pool
> > > B that is of type 'Scratch', then Pool A can take a volume from Pool B.
> > > If it was unable to do that, it falls back to trying to take a volume
> > > from the pool named 'Scratch'.
> > > When it is autopruning, it can cause volumes with a RecyclePoolId
> > > pointing to the same Scratch Pool as the current Pool's RecyclePoolId
> > > to be pruned/purged and moved into that Scratch Pool.
> >
> > I'm not sure that it is a good idea, RecyclePool and ScratchPool are two
> > different things. We can see that like a cycle.
>
> Note that Graham said the suggested new behaviour is only triggered if you
> define the pool targetted by RecyclePool as having Pool Type = Scratch.
> If you leave it as an ordinary Backup pool, as it would be in your example,
> the behaviour is the same as before.

I found this not very simple, try to write the manual part that will explain 
that. And it links together two different things (RecyclePool and 
ScratchPool). I still think that the previous Pool->ScratchPool directive is 
the most simple. Easy to explain, easy to use.

> The existing behaviour for the recommended RecyclePool = Scratch set-up
> is also preserved by this change.  At the moment, the scratch pool is
> magic because it is named 'Scratch', but after the change, it behaves
> in this special way because it is Pool Type = Scratch, which seems rather
> more obvious.

I don't think that it's time to use PoolType field, not for this application 
or not like that.

> In fact, if we could be sure people followed the documentation, we
> could remove any special handling of the pool name 'Scratch' entirely.
> However, this would change the behaviour of existing configurations
> that use RecyclePool = Scratch but declare the Scratch pool to have
> Pool Type = Backup.  Although that's not the documented way to do it,
> the Pool Type doesn't seem to matter, so people could be doing that wrong
> and not notice.  Hence Graham's change keeps the special behaviour of
> the name 'Scratch' as a fall-back.

In any cases, we have to keep the Scratch pool as it is, and Graham patch is 
pretty cool for that (Pool.Name = Scratch, PoolId = ScratchPoolId in 
get_volume_from_scratch())

Thanks for comments

Bye


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