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


Hello Graham,

Le Monday 24 November 2008 11:02:27 Graham Keeling, vous avez écrit :
> Hello,
>
> Using bacula-2.2.8 (though I've had a brief look at SVN, and it seems the
> same)...

So, please, provide your patch against the current trunk... We need also a 
documentation patch for this feature. You can send it to me in a text format 
if you are not a LaTeX user. A regress script that tests all new options is 
also welcome.

> I configured bacula with a single storage daemon, using disk file volumes.
> I configured my pools to have RecyclePool = Scratch, with the intention
> that the volumes would be recycled throughout all of the pools.
>
> Eventually, I got this working, so I went on to the next step - having
> multiple storage daemons in different locations.

One advise maybe, use different MediaType for each location, and bacula will 
do the work...

> 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.

> The effect would be that a file 
> would be left on disk in one location, whilst a new version of it would
> appear in another.
> This was clearly because I was using a global Scratch pool.
>
> What I would like to do is set up an individual Scratch pool for each
> of my storage devices, so that the media in one location stays in that
> location.
>
> After looking at the bacula code, it seems to me as if the configurable
> Scratch pool feature was planned and it has nearly been implemented.
> It is possible to set 'Pool Type = Scratch' in a Pool, and 'ScratchPoolId'
> is a database field on Pools and Media - though it is always set to 0. The
> current 'RecyclePoolId' tells media where they should go when they are
> recycled, but Media are only drawn from the Pool specifically named
> 'Scratch'. I've even come up with patches to the (2.2.8) code that seem to
> have the ScratchPoolId working in the way that I assume it was intended.
>
> 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....

> It seems more elegant than needing to give a different 
> Media Type for every different storage.

I'm agree, but it works well, and permit to share pool, scratch etc...


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 ?

Bye

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