CA Disk provides several options that can prove beneficial in managing IMS/VS databases that consist of VSAM data sets. The ARCHIVE (BACKUP) and RESTORE functions can be used as a backup alternative to IBM's image-copy utility. The speed of CA Disk processing and the data compression feature provide savings in both time and space. If directed to disk, substantial disk space is saved. If directed to tape, both the number of tape mounts (operator intervention) and the quantity of tapes used can be reduced substantially.
You can also use IBM's image-copy and direct its output to disk, thus avoiding operator intervention, and then use either the sequential migrate to tape function or the archive function to consolidate several disk data sets onto a single tape.
In order to produce a valid backup copy of an IMS/VS database, all of the data sets that comprise the database must be backed up individually. It is important that no updating be allowed to occur against the database until the backup of all of its component data sets has completed. If updating should take place before a complete database backup is obtained, a loss of synchronization between the various portions of the database can result if a recovery is attempted. Appropriate care must be exercised when establishing backup procedures to ensure that all of the related database data sets are identified.
The IMS/VS Backout or Recovery Utility has been changed to use the key values, instead of the RBA pointers, during recovery. Therefore, no extra considerations are necessary when using CA Disk to back up and restore IMS/VS databases. This is because the automatic reorganization CA Disk does at restore time no longer presents a problem for the IMS/VS Backout or Recovery Utility.
IMS databases do not have alternate indexes as defined by VSAM. The secondary indexes in an IMS database are actually separate KSDS clusters that IMS updates as an index. When an IMS database is initialized, each CI is formatted and appears to VSAM (and also to CA Disk, image-copy and IDCAMS) to contain a single logical record. This logical record/CI is updated by IMS. As updates are made to the database, these indexes can undergo CA/CI splits.
Whenever an IMS cluster is moved or restored, take care to ensure that the CI size is not changed. Default parameters prevent CA Disk from changing the CI size. The CI size can be changed inadvertently by unknowingly requesting a CI size change in the RESTORE command. It can also be changed by VSAM allocation routines when the CI size is invalid for the device type being used. Any change in CI size will destroy the IMS database unless specifically planned and accounted for by the database administrator. Therefore, do not specify sysparm VSATTRIB, which allows IDCAMS to select a CI size every time the cluster is defined, when processing IMS databases.
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