How do Job Priories work

[Leecabs]

using netbackup 6.5.4 on unix

scenerio

I've got 10 jobs queued waiting for tapes all on job priority 10

I kick of a manual backup of an existing policy it also has a priority of 10 - once queued I change the priority to 100. Problem is the 10 jobs that were queued start before the 100 priority job.

How exactly does job priority work as I read the manual and it's still confusing.

[Marianne]

If you change priority AFTER the job has been submitted, it will have no effect on the queued job.

Priority setting in policy is only checked when the job gets submitted.

[Andy_Welburn]

is queued awaiting resources that aren't currently available (e.g. tapes etc)  then it will remain queued until such time as they are. Those at a lower priority will continue to run first if their resources are currently available (e.g. tape loaded in drive).

[Leecabs]

ok so if the priority is changed after its been submitted it has not effect - odd why it lets you change it then?

Also, if I had changed the priority before i submitted the job would the job have gone straight to the top of the queue in front of other jobs waiting with lower priority - I know i can test this but the OPS guys say this does not happen either.

[Andy_Welburn]

It will have an effect if resources become available - if resources become available for all queued jobs (e.g. tape drive becomes free) then that with the highest priority will go first.

"if I had changed the priority before i submitted the job would the job have gone straight to the top of the queue in front of other jobs" - not necessarily - it depends again on whether resources are available for it to take priority & once more as resources become available it will take priority.

***EDIT***

All things being equal, if all queued jobs are awaiting the same resource then that with the highest priority will start first/next. A job with a higher priority will not cause lower priority jobs to suspend or cancel so that it can start - it will wait for resources.  The only way you could accelerate this would be to suspend all the queued & running jobs that are preventing or liable to prevent the high priority job from starting.

[Leecabs]

the reason jobs are sitting queued is that they are waitiing for a free tape drive. All jobs are waiting for the same "resource" so as soon as that resource comes free then the job with the highest priority should start???

[Andy_Welburn]

Imagine an environment with one tape drive & two tapes.

Jobs are queued & running with normal priority to the tape drive & tape 1.

A higher priority job is started (or one of the above queued jobs is amended to a higher priority) that requires the same tape - it will be the next job to start (limit here would be the number of streams to the drive)

If a new higher priority job is started that requires tape 2 then it will queue until such time as all the other jobs have finished. This is because the resource, tape 1, is already loaded & will remain so until all the jobs utilising it have completed.

[RiaanBadenhorst · Accepted solution]

I think there is some confusion here about where you're changing the job priority. It can be done on the policy, which I believe is what Marianne is referring to. But i suspect what you're referring to is changing it in the activity monitor??

From the Admin guide...Pay attention to the three scenarios.

Understanding the Job Priority setting
NetBackup uses the Job Priority setting as a guide. Requests with a higher priority do not always receive resources before a request with a lower priority.
The NetBackup Resource Broker (NBRB) maintains resource requests for jobs in a queue.
NBRB evaluates the requests sequentially and sorts them based on the following criteria:
■    The request's first priority.

■    The request’s second priority.
■    The birth time (when the Resource Broker receives the request).

The first priority is weighted more heavily than the second priority, and the second priority is weighted more heavily than the birth time.
Because a request with a higher priority is listed in the queue before a request with a lower priority, the request with a higher priority is evaluated first. Even though the chances are greater that the higher priority request receives resources first, this is not always definite.

The following scenarios present situations in which a request with a lower priority may receive resources before a request with a higher priority:
■    A higher priority job needs to unload the media in a drive because the retention level (or the media pool) of the loaded media is not what the job requires. A lower priority job can use the media that is already loaded in the drive. To maximize drive utilization, the Resource Broker gives the loaded media and drive pair to the job with the lower priority.
■    A higher priority job is not eligible to join an existing multiplexing group but a lower priority job is eligible to join the multiplexing group. To continue spinning the drive at the maximum rate, the lower priority job joins the multiplexing group and runs.
■    The Resource Broker receives resource requests for jobs and places the requests in a queue before processing. New resource requests are sorted and evaluated every 5 minutes. Some external events (a new resource request or a resource release, for example) can also trigger an evaluation. If the Resource Broker receives a request of any priority while it processes requests in an evaluation cycle, the request is not evaluated until the next evaluation cycle starts.

[Andy_Welburn]

[Leecabs]

I'd had a go at reading the documentation but your explaination solves it so thanks!!!!