13.6.5 BLOCKSIZE Specifier

The BLOCKSIZE specifier indicates the physical I/O transfer size for the file. It takes the following form:

BLOCKSIZE = bks

bks
Is a scalar numeric expression. If necessary, the value is converted to integer data type before use.

If you specify a nonzero number for bks, it is rounded up to a multiple of 512 byte blocks.

If you omit BLOCKSIZE= or specify zero for bks, the filesystem default is assumed.