The SUBBLOCKSIZE option applies only to embedded ordered data sets. The SUBBLOCKSIZE and TABLESIZE keywords are synonyms only when they apply to embedded ordered data sets. Blocks within ordered data sets can be divided in two or more subblocks. The size of each subblock is always an integer multiple of the value assigned to the SUBBLOCKSIZE option. The subblock size must be greater than or equal to the record size of the data set, and it must not exceed half of the block size. The subblock size is always expressed in the same units as the block size.

If the subblock size is not specified, blocks are not divided in subblocks.