Database backup copies

When IMS takes a regular system checkpoint, it records internal control information for DL/I and for Fast Path, but it does not record any of the contents of the database. If the database is lost, examining the last system checkpoint does not allow you to recover it. The system log can tell you what changes have occurred, but without the original database itself, recovery can be impossible.

Recommendation: Make a backup copy of all databases after you initially load them. You should also make new backup copies at regular intervals. More recent backup copies require fewer log change records to be processed during recovery, and thus the time needed for recovery is reduced.

IMS provides several utilities for making backup copies of a database:

Image copy utilities
The IMS database image copy utilities allow you to take a snapshot of a database before and after changes have been to the database. These snapshots are called image copies.

Definition: An image copy is an as-is image of a database. The image copy utilities do not alter the physical format of the database as they copy it. Image copies are backup copies of your data that help speed up the processes of database recovery and backout.

The image copy utilities are Database Image Copy utility (DFSUDMP0), Database Image Copy 2 utility (DFSUDMT0), and Online Database Image Copy utility (DFSUICP0).
The HISAM Reorganization Unload utility (DFSURUL0)
This utility allows you to process an entire HISAM database in one pass (the image copy utilities process each database data set individually) while it is unloaded and reorganized. This utility runs while the database is offline.

Recommendation: Make an image copy of the database before unloading it. You can use the image copy for recovery purposes if a failure occurs in the unloading process. You can also create an equivalent of an image copy data set without using the HISAM Reorganization Reload utility.

After you unload the database, you use the HISAM Reorganization Reload utility (DFSURRL0) before bringing the database back online. If you do not reload the database, an application program can use the database, but will use the old organization of the data set. Your backup copy will not match the log records produced for the database, and you will not be able to use the backup copy to recover the database without damaging your data integrity.

You can run these utilities with or without DBRC. You can also use various z/OS® utilities to make your backup copies, but these utilities do not interact with DBRC, which could cause integrity problems depending on how your IMS system is defined.