Image copy utilities (DFSUDMP0, DFSUDMT0, DFSUICP0)

IMS enables you to take a picture of your database before and after changes have been made to the database. The pictures are called image copies. The term refers to the fact that the copy is an as-is image; 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 process of database recovery.

The Database Image Copy utility (DFSUDMP0), Database Image Copy 2 utility (DFSUDMT0), and Online Database Image Copy utility (DFSUICP0) create image copies of databases. All of the image copy utilities operate on data sets or DEDB areas, so if a database is composed of multiple data sets or areas, be sure to supply the utility with multiple specifications. You can request that one of the supported image copy utilities produce both an image copy data set and a duplicate image copy data set in one run of the utility.

Recommendation: Copy all data sets or areas belonging to a database at one time. If you perform multiple recoveries in order to reset a database to a prior state, recover all data sets belonging to the database and to all logically related databases (including those related by application processing) to the same point to avoid integrity problems.

Each of the image copy utilities provide the option to create backup copies without taking databases and areas offline. You can use this capability to provide increased database availability. Image copies taken while the database is available for concurrent update processing by IMS applications are called concurrent image copies or fuzzy image copies. Changes already made to the database by active applications might be missing from the copy because the changes might not have been physically written to the data set. These changes, however, have been written to the log. In this case, it is necessary to go back to some earlier point in the logs to ensure that all changes are applied. How far to go back depends on the type of database and which image copy utility was used.

When concurrent copy or fast replication image copies are not used, the database must be either taken offline or made available only for 'read' access and a consistent or 'clean' image copy is taken. See Concurrent image copy for more information.

If the image copy was made while the database was not being accessed for update, only changes that were logged after the run time of the copy are required.

When using these utilities, you have the option of creating one to four output image copies. Only the Database Image Copy 2 utility allows three or four output copies and only the first two output copies are recorded in the RECON data set. When the Database Image Copy 2 utility uses the DFSMSdss fast replication function, only one output copy is created.

The advantage of making multiple copies is that if an I/O error occurs on one copy, the utility continues to completion on the other copies. Also, if one copy cannot be read, you can perform recovery using another. The trade-off in deciding whether to make multiple copies, is that performance can be degraded because of the time required to write the additional copies.

DBRC works similarly with the three image copy utilities. When the DFSMSdss fast replication function is not used, the rules for pre-definition and reuse of image copy data sets apply to all three. Each utility calls DBRC:

An image copy record in the RECON data set has the same format whether its corresponding image copy data set was created by the Database Image Copy utility, the Database Image Copy 2 utility, or by the Online Database Image Copy utility.

Two different commands create image copy jobs:

When you run batch jobs without logging, take an image copy immediately afterwards; do not count on rerunning the batch jobs, as part of a subsequent recovery, in combination with the Database Recovery utility. The database could be damaged by the combination because the batch processing is not guaranteed to be physically repeatable.