RCU overview

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A copy of the RECON must be made and modified to match the data sets that exist at the recovery site to perform valid recoveries. RCU will create a clean copy of the RECON data sets at a particular point in time for recovery.

In general, a recovery site contains all the data that is needed to restore IMS databases to a known active site time. The following data is needed for recovery:
  • Image copy data sets taken at the active site
  • IMS log data from the active site (logs, change accumulation data sets, or both)
  • A RECON that accurately reflects the activities that have taken place at the active site

Image copies

Database recovery works at the database data set (DBDS) level; each DBDS needs to be restored individually and starts with an image copy. Restoring an image copy creates an exact copy of the DBDS to a known time. Image copies can be concurrent (also called fuzzy) or non-concurrent. Non-concurrent image copies are usually called batch image copies. When a concurrent image copy is used, log data from before the time that the image copy was taken is usually needed. Batch image copies require only the log data that was created after the image copy was taken. Most image copy utilities take a primary and secondary copy (two copies in one pass). Often it is the secondary copy that is shipped to a recovery site. Information about image copy data sets is normally retained by DBRC.

After a DBDS has been restored by using an image copy, you must apply all of the changes that have been made since the image copy was taken. IMS log data sets are read to determine what changes have been made.

IMS log data

IMS keeps a log of all of the changes that are made to databases. This log is written to data sets that are called online log data sets (OLDS), system log data sets (SLDS), and recovery log data sets (RLDS). A SLDS contains all of the log data that was written by IMS. An RLDS is a subset of the SLDS and contains only the log data that is needed for database recovery. Information about log data sets is maintained by DBRC. Like image copies, there can be primary and secondary log data sets. Often the secondary copy is shipped to a recovery site. No IBM® recovery utility uses an OLDS as input.

A change accumulation data set also contains log data that is usable by a recovery utility. The Change accumulation (CA) utility reads log data sets and reformats the data to a form that is more efficient for recovery utilities. The CA utility does not create a secondary copy. Information about CA data sets is kept by DBRC.

RECON data sets

RECON data sets must exist at the recovery site. Often, a copy of the RECON data sets that are taken at the active site are shipped to the recovery site. One method of making a copy of the RECON data sets is by using the DBRC BACKUP.RECON command.