Parallel restore operations

You can perform restore operations while using more than one device simultaneously. The data that you restore in this manner must have been saved in parallel format.

You can use the Restore Library (RSTLIB), Restore Object (RSTOBJ), and Restore (RST) commands with a media definition to perform a parallel restore. You can use a media definition with the RSTLIB command to restore *ALLUSR, *IBM, and *NONSYS libraries that were saved with a media definition.

Restoring from a parallel save is typically faster. This is usually true when restoring an entire library or restoring any objects that were saved near the start of a given tape file than restoring from a serial save operation. However, there are cases where restoring individual objects from a parallel save can take significantly longer than restoring from a serial save operation. This situation can occur if the object to be restored is near the end of the tape file

You can restore from a parallel save if you are using fewer devices than the save operation used. However, IBM® does not suggest this, due to the amount of volume switching that you will need to do. IBM also does not suggest this due to performance reasons. If you are restoring files with constraints, you must use the same number of devices for the restore as you used for the save. Restore operations that use fewer drives should only be used to restore individual objects. Restore operations that use fewer drives should never be used as part of a system recovery strategy, or to restore large amounts of data. Whenever possible, the same number of devices that were used during the save operation should be used during a restore operation.

A Display Tape (DSPTAP) command displays the list of objects that the system saves across all media files. You only need one media file to display all of the objects that the system saved during a parallel save operation. This list also displays the number of media files that you need to restore data. However, you need all of the media files to restore any of the objects that the system saved. This might include multiple volumes.

IBM suggests that you use the same media definition object when saving and restoring the same objects. If you use a different media definition object when restoring, make sure that the same number of media files are defined within that media definition object. If the number of media file definitions is different from the number that exists on the storage media, you will receive an error message.