Disabling the sharing of NetBackup reservations

In NetBackup, shared reservations are enabled by default.

See Sharing reservations in NetBackup.

In most cases, sharing reservations results in better performance.

In this case, without shared reservations, one job runs and other jobs requiring the same media are queued because they cannot get a reservation. With shared reservations, the jobs can start simultaneously. However, with a limited set of resources (media/drive pair or disk drives), resources may bounce or "ping-pong" between different jobs as each job requests the resource.

For example, assume the following:

Two duplication jobs, job 1 and job 2, are duplicating backup images. Job 1 is duplicating images 1 through 5, and job 2 is duplicating images 6 through 9. The images are on the following media:

In this example, both jobs require access to media A2. Without shared reservations, if job 1 gets the reservation first, job 2 cannot start, because it needs to reserve media A2. A2 is already reserved by job 1. With shared reservations, both jobs can start at the same time.

Assume, however, that only a few drives are available for writing. Also assume that job 1 begins first and starts duplicating image 1. Then job 2 starts using media A2 to duplicate image 6. Media A2 in effect bounces between the two jobs: sometimes it is used by job 1 and sometimes by job 2. As a result, the overall performance of both jobs may degrade.

You can use the following procedure to disable the sharing of reservations.