How to Perform Parallel and Concurrent Recoveries

You can recover data by using serial, concurrent, or parallel restore operations. If BRMS performed your saves as serial or concurrent backups, BRMS can restore them either serially or concurrently. On the other hand, however, you can perform parallel retrieves only if BRMS used a parallel operation to perform the save. Both concurrent and parallel restore operations require multiple tape drives.

Following are brief summaries of the characteristics of, and the differences between, serial, concurrent and parallel recoveries.

Serial Recovery

This straightforward recovery method is the simplest way to recover data that was saved by multiple control groups. In a serial recovery operation, BRMS issues one recovery job at a time to one tape drive. BRMS performs serial restores in a sequential manner, by restoring one tape and one control group after another. By default, BRMS considers every save and restore a serial operation unless otherwise specified by you.

Concurrent Recovery

In a concurrent recovery operation, you send multiple recovery jobs to multiple tape drives to process at the same time (concurrently). You, not BRMS, set up the concurrent recovery. To do this, try to evenly balance the size of the jobs so that they end at the same time. Concurrent recovery operations can reduce your downtime after a system failure by allowing you to recover multiple libraries or objects at the same time.

Parallel Recovery

BRMS will restore a saved item sequentially. However, if the saved item was saved using parallel save/restore (spreading a single object), BRMS will use the number of resources you specify up to the number of resources used to save the item. A saved item cannot be restored using parallel recovery if the object was not saved using parallel.

To perform a parallel restore of a saved item from fewer resources that were used for the save, a media library is recommended because of the additional media mounts that may be required.