Improving performance of CDS and journal backup

System performance is directly related to the time it takes to back up the control data sets and the journal, because all DFSMShsm activity and all JES3 setup and initialization activity is suspended while these important data sets are backed up. By improving the performance of CDS and journal backup, you can decrease the time that system-wide serialization is in effect.

To decrease the time required to back up the control data sets and the journal, consider any or all of the following:

Use the non-intrusive journal backup method. This method allows DFSMShsm activity to continue while the journal is backed up. For more information about the non-intrusive journal backup method, see the topic about using non-intrusive journal backup in z/OS DFSMShsm Storage Administration.
Activate XCF and specify PLEXNAME via the SETSYS command for each of your multi-host DFSMShsm systems. For more information, see the SETSYS command in z/OS DFSMShsm Storage Administration.
Back up the control data sets using concurrent copy by allocating them on SMS-managed, concurrent-copy-capable devices (does not apply to the journal) and specifying DATAMOVER(DSS). Ensure that they are associated with a management class BACKUP COPY TECHNIQUE attribute of REQUIRED(R), PREFERRED (P), VIRTUALREQUIRED (VR), VIRTUALPREFERRED (VP), CACHEREQUIRED (CR), or CACHEPREFERRED (CP).
Modify the block size for CDS backup version data sets.
Preallocate DASD backup data set copies with a block size equal to one-half the track size of the DASD device. For example, the half-track capacity of a 3390 device is 27␠998.

If the keyword BLKSIZE is specified on the pre-allocated DASD backup data set copies, it must be in the range of 7892 to 32␠760 inclusive.
Back up the control data sets in parallel.
If you are backing up your control data sets to DASD (BACKUPDEVICECATEGORY(DASD)), the control data sets are always backed up in parallel.
If you are backing up your control data sets to tape (SETSYS BACKUPDEVICECATEGORY(TAPE)), control data sets are always backed up in parallel when you:
- Specify DATAMOVER(DSS)
- Specify DATAMOVER(HSM) and specify the TAPE(PARALLEL) option of the CDSVERSIONBACKUP command. If you choose parallel backup to tape, ensure that one tape drive is available to backup each CDS cluster and another tape drive is available to backup the journal data set.
  Requirement: If a CDS is a multicluster CDS, then you need additional tape drives.
  
  For more information about the TAPE(PARALLEL|NOPARALLEL) option of the SETSYS CDSVERSIONBACKUP command, see the SETSYS command in z/OS DFSMShsm Storage Administration.

Table 1 shows the interaction of the BACKUPDEVICECATEGORY and DATAMOVER subparameters in defining the parallel backup environment for control data sets.

Table 1. Backing up the control data sets in Parallel
Subparameters of the SETSYS CDSVERSIONBACKUP command	RESULT
BACKUPDEVICECATEGORY (DASD) DATAMOVER(HSM)	Parallel backup, preallocate backup data sets
BACKUPDEVICECATEGORY (DASD) DATAMOVER(DSS)	Parallel backup, preallocate backup data sets
BACKUPDEVICECATEGORY (TAPE) DATAMOVER(HSM)	No parallel backup unless you specify TAPE(PARALLEL)
BACKUPDEVICECATEGORY (TAPE) DATAMOVER(DSS)	Parallel backup, allocate a tape drive for the journal and one for each CDS cluster