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


Hello,

On Thu, Dec 11, 2008 at 10:22:42AM +0100, Eric Bollengier wrote:
> > I found that volumes would go through the Scratch pool, and be shared out
> > among all the different storage daemons.
> 
> I'm quite suprised, we have also a StorageId that should prevent this
> problem. 
> This is not perfect, but it should work in this situation.

I have just tested this again with both bacula-2.2.8 and bacula-2.5.16-beta,
and the StorageId does not prevent it happening, so I think that it is broken
somehow.
Perhaps because all the places that check StorageId are only doing so if
InChanger=1. I don't think InChanger is ever 1 for me, because I am not using a
disk changer.

> > So, my question is whether I am right in assuming that the ScratchPoolId on
> > Pools was intended to be used this way (to indicate a pool to draw media
> > from), or whether there is a reason (or reasons) that the implementation
> > was not finished.
> 
> We were waiting for your patch :) It's a good idea to add database fields for 
> future use, that avoids schema upgrade between each release....

Haha!

> I've take a look of your patch, and i it looks quite good. (i've seen 2 small 
> typo problems in sql_create.c (ed4) and in ua_update.c (recyclepool))
> 
> But i think that your patch can be more simple, let me explain
> 
> I think that you want that a pool (dedicated to a storage) takes media from a 
> specific Scratch pool. So, it's a pool attribute. (We have the ScratchPoolId 
> field in the Media table, but it's not a reason to use it).
> 
> It's not like the RecyclePool attribute that is a Volume attribute (for life).
> The ScratchPool is used to select a volume from a pool, and the RecyclePool is 
> used to put a volume in a pool.
> 
> If i'm not wrong and you are ok, can you cleanup your patch in this way ?

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 will send my patch for this, which applies to SVN revision 8139, as soon
as I have confirmed with my office that the FSFE form has been sent.

Graham.


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