Re: [Bacula-users] Multiple drives in changer

On Fri, Apr 2, 2010 at 2:44 AM, Matija Nalis <mnalis+bacula AT carnet DOT hr> wrote:

On Thu, Apr 01, 2010 at 08:49:43AM -0600, Robert LeBlanc wrote:
> I have two LTO-3 drives in a changer and three LTO-3 pools. Earlier version
> of Bacula would try to use an empty drive before unloading a drive when a
> tape from a different pool was requested. I used to also be able to run in
> parallel migration jobs from two different pools at the same time. Since
> moving to 5.0.1, my second drive goes unused. Is there some change in the
> code that prevents this behavior?

I think you need to set
Prefer Mounted Volumes = no

to get old behaviour (maximum parallelism).

Note however that it might lead to deadlocks (or at least, it could
in the past... don't know if that was fixed).

Prefer Mounted Volumes = <yes|no>

If the Prefer Mounted Volumes directive is set to yes (default yes), the Storage daemon is requested to select either an Autochanger or a drive with a valid Volume already mounted in preference to a drive that is not ready. This means that all jobs will attempt to append to the same Volume (providing the Volume is appropriate -- right Pool, ... for that job). If no drive with a suitable Volume is available, it will select the first available drive. Note, any Volume that has been requested to be mounted, will be considered valid as a mounted volume by another job. This if multiple jobs start at the same time and they all prefer mounted volumes, the first job will request the mount, and the other jobs will use the same volume.

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.

I guess this is where we need clarification about what is an available drive. I took this to mean a drive that has no tape is more available, and then a drive that does already have a tape mounted would be next in availability. It seems that as long as no job is writing to that tape, then the drive is available. I do want this setting to yes and not no, however, I would like to minimize tape changes, but take advantage of the multiple drives.

Robert LeBlanc
Life Sciences & Undergraduate Education Computer Support
Brigham Young University

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