On 05/03/2013 02:53 PM, Josh Fisher wrote:
> 
> On 5/3/2013 1:37 PM, Dimitri Maziuk wrote:

>> Ideally one should be able to specify multiple Device's in the Storage
>> and have bacula write to them in turn until all get full. A couple of
>> extra "for" loops and another list is basically all it takes to support
>> that, so I'm slightly surprised it's not there already.
> 
> Well, I think it is quite a bit more complicated than that. Bacula is 
> designed with a tape paradigm. With tape drives, the device doesn't 
> change. but rather another volume is swapped into the same device.

It's the 'single tape' paradigm. I've a couple of 10yo (I think)
qualstar jukeboxes here with 12 tape slots and 2 drive slots in each.
(Although we never added the 2nd drive to either of them.)

 So,
> Bacula does device assignment one time when the job is started. The 
> reason is because Bacula is multi-threaded and it is the simplest way to 
> avoid race conditions caused by device contention. What you are 
> considering would require a new device assignment each time a new volume 
> is needed. While possible, it is way more complex that it appears at 
> first glance.

Fair enough. So what happens when a new volume is needed and there's no
room on the current device? -- this is the point where you'd switch to
the next device in the list and try again until you run out of devices.

-- 
Dimitri Maziuk
Programmer/sysadmin
BioMagResBank, UW-Madison -- http://www.bmrb.wisc.edu

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