For TAPE data sets utilizing SMS, zero blocksize must be coded on the FILE statement.
When blocksize is not coded on the file statement, the system uses 1-to-1 blocking which increases run time and slows down the performance.
Below are examples of the variations of SMS usage.
FILE file-name FB(0 0)
This specifies to pick up the LRECL from the JCL and to utilize the block size set by System Management Storage (SMS).
FILE file-name FB(150 0)
This specifies to pick up the LRECL from this definition and to utilize the block size set by SMS.
FILE file-name FB(150 3000)
This specifies to pick up this definition and ignore both the JCL and the SMS determined block size.