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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.
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.