Large tape blocks have two advantages:
They increase the degree of tape utilization due to the smaller number of gaps.
They improve the throughput when saving to tape, thus speeding up tape processing.
The tape block size can be selected via the BLOCKING-FACTOR operand for each statement or as an archive attribute. In addition, the tape block size can be selected globally using the ARCHIVE parameter BLOCK-SIZE-TAPE (for long tapes) and BLOCK-SIZE-T-C (for MTC devices).
BLOCKING-FACTOR=*STD
Specifying *STD (the default) selects the blocking factor as follows:
The blocking factor from the archive definition applies for statements in which the archive is specified. If *STD (default when the archive is created) is also specified there, the settings of the global ARCHIVE parameters apply.
The settings of the global ARCHIVE parameters apply for statements in which no archive is specified.
By default a block size of 256 Kbyte (BLOCK-SIZE-T-C=BIG) is set in the parameter file SYSPAR.ARCHIVE.<vers> for MTC devices. For devices which do not support this block size (emulated tape devices, T9G), ARCHIVE automatically uses a block size of 32 Kbyte. Save files are updated with the tape block size used to date.
BLOCKING-FACTOR=*MAX
The specification *MAX selects the maximum blocking factor possible in the current BS2000 version. Currently the maximum value is 128 (block size 256 Kbyte). A block size of 256 Kbyte also corresponds to the maximum block size for the tape devices currently released Save files which are written with the maximum value of a BS2000 version cannot be read in an earlier BS2000 version which does not support this blocking factor.