The SETSYS CDSVERSIONBACKUP subparameter DATAMOVER allows you to
indicate which of the following datamovers that DFSMShsm can use to
back up the control data sets. (The DFSMShsm journal is always backed
up by sequential I/O.)
- DATAMOVER(DSS) — tells DFSMShsm to use DFSMSdss logical
dump to back up the control data sets
- DATAMOVER(HSM) — tells DFSMShsm to use IDCAMS EXPORT to
back up the control data sets
When you use DFSMSdss—rather than IDCAMS—to copy the
data, concurrent copy can be used, and the control data sets will
be validated as they are backed up. Concurrent copy allows the CDS
backup to complete as soon as the journal has been backed up, so that
DFSMShsm can begin processing requests before the CDS backups are
completed.
Rule: If you access the control data
sets in RLS mode, you must use DFSMSdss as the data mover.
If you use IDCAMS, you need to examine the number of records copied
each day (check the record count in message IDC0005I from IDCAMS EXPORT),
because a broken VSAM index for a CDS will likely result in significant
data loss in the backup copy. This loss can go unnoticed for a considerable
period of time.
Recommendation: DFSMShsm development
strongly recommends that you specify DATAMOVER(DSS), which provides
advantages of validation during backup as well as (with the concurrent
copy function) reduced serialization of the control data sets. DATAMOVER(HSM)
is retained as an option for purposes of coexistence with previous
releases.