On 2014-11-19 12:46, Ana Emília M. Arruda wrote:
> Hi Mike,
> 
> On Tue, Nov 18, 2014 at 5:53 PM, Brady, Mike
> <mike.brady AT devnull.net DOT nz> wrote:
> 
>> On 2014-11-19 08:52, Ana Emília M. Arruda wrote:
>>>>> Do you have "prefer mounted volumes" set to no in your jobs
>>>>> definition? It is recommended if you are using multiple devices
>>>>> and
>>>>> one pool.
>>>> 
>>>> I do not have this set because of the warnings against it in
>> both
>>>> the manual and one of the white papers.
>>> 
>>> ​But this is recommended when using multiple devices
>> (autochanger or
>>> stand alone) and one pool.​
>>> 
>> 
>> The warning in the manual sounds quite serious. Is it no longer
>> valid?
> 
> ​Yes, it is still valid. Maybe I was not very clear in my answer.
> The white papers talk about having this directive set to "no" to
> spread jobs over multiple devices instead of using maximum concurrent
> jobs directive when having multiple pools. Because it can lead to this
> situation: "As this option will try to spread Jobs over all devices,
> if you are using multiple Pools in your backup strategy, all devices
> can be busy writing to Pool A, and other Jobs that want to use
> something else will wait for a free slot. " (from the whtie paper).

I did not take the sections in the white paper to be mutually exclusive. 
Meaning that I did not take it to mean that you used either "maximum 
concurrent jobs" or "prefer mounted volumes".  Perhaps that is one of 
many points that I am missing :-)

> 
> ​I'm supposing you have scheduled jobs in a way that they will use
> just one pool in a specific day. So all of your jobs will use volumes
> in just one pool and, in this case, the prefer mounted volume
> directive set to "no" is recommended,​
> 
Correct.  Normally only one of the IncPool, DiffPool or the FullPool is 
used on any given day.  Occasionally the FullPool is used on a day when 
the IncPool or DiffPool is used.  If the job that needs a FullPool 
volume needs to wait, that is OK.

>  I'm not sure if you had a took at the manual:
> "If the directive is set to NO, the Storage daemon will prefer finding
> an unused drive, otherwise, each job started will append to the same
> Volume (assuming the Pool is the same for all jobs). Setting Prefer
> Mounted Volumes to no can be useful for those sites with multiple
> drive autochangers that prefer to maximize backup throughput at the
> expense of using additional drives and Volumes. This means that the
> job will prefer to use an unused drive rather than use a drive that is
> already in use.
> 
> Despite the above, we recommend against setting this directive to NO
> since it tends to add a lot of swapping of Volumes between the
> different drives and can easily lead to deadlock situations in the
> Storage daemon. We will accept bug reports against it, but we cannot
> guarantee that we will be able to fix the problem in a reasonable
> time.
> 
> A better alternative for using multiple drives is to use multiple
> pools so that Bacula will be forced to mount Volumes from those Pools
> on different drives."
> 
Yes, I have read this many times and I quote

"can easily lead to deadlock situations in the Storage daemon"

I take this to mean a logic deadlock in the SD which potentially means 
that backups will stop (a very bad thing that is not acceptable to me).  
Or is this just talking about the multiple pool situation where jobs may 
have to wait if all the devices are busy with volumes from other pools 
(an acceptable thing for me)?

> ​
> ​Have you tried to set it to no just to notice if the problem of the
> second job waiting for the volume still occurs?

No I have not tried it given the above.

In your previous email in reference to "prefer mountable volume" you 
said

"But this is recommended when using multiple devices (autochanger or 
stand alone) and one pool.​"

Where is this recommended?  Every reference that I can find (manual and 
white paper) recommends against its use without caveats and recommends 
using "Maximum Concurrent Jobs" instead.

Thanks

Mike

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