OPTIMUMDASDBLOCKING and NOOPTIMUMDASDBLOCKING: Specifying whether DFSMShsm should use its defined optimum block size

Explanation: OPTIMUMDASDBLOCKING | NOOPTIMUMDASDBLOCKING are mutually exclusive, optional parameters indicating whether DFSMShsm should use its defined optimum block size when outputting or recovering to DFSMShsm-owned DASD. Optimum blocking refers to DFSMShsm writing its output or input in blocks that are multiples of 2 KB and is determined by the device’s track size for data being written to DFSMShsm-owned DASD. For example, all models of 3390 DASD have the same track length and an optimum block size of 18 KB (1 KB equals 1024 bytes). This permits better use of space on DFSMShsm-owned DASD devices.

OPTIMUMDASDBLOCKING indicates to DFSMShsm to use its defined optimum block size when writing to DFSMShsm-owned DASD.

NOOPTIMUMDASDBLOCKING indicates to DFSMShsm to not use its defined optimum block size when writing to DFSMShsm-owned DASD. DFSMShsm writes to DFSMShsm-owned DASD in 2 KB blocks.

SMS relationship: Parameter has the same meaning when applied to SMS-managed or non-SMS-managed DASD volumes or data sets.

SETSYS default: None.

DFSMShsm default: If you do not specify the NOOPTIMUMDASDBLOCKING parameter on any SETSYS command, DFSMShsm uses its defined optimum block size when writing to DFSMShsm-owned DASD as the default.

Note:

OPTIMUMDASDBLOCKING does not pertain to small-data-set-packing data sets, dump VTOC copy data sets, or backup VTOC copy data sets.
You can change this parameter while DFSMShsm is running. The change takes effect when the next data set destined for DFSMShsm-owned DASD is opened for output.