OPEN tests the JFCB for each data set after the one being opened. The JFCB contains information coded when the data set was allocated and information that OPEN can have stored there before it was dynamically reconcatenated.

All of the above processing previously described occurs for any data set that is acceptable to BSAM. The OPEN that you issue does not read tape labels for data sets after the first. Therefore, if there is a tape data set after the first that has a block size larger than all of the prior specifications, the BLKSIZE value must be specified on the DD statement. The system later reads those tape labels but it is too late for the system to discover a larger block size at that time.

For each data set whose JFCB contains a block size of 0 and is on permanently resident DASD, OPEN obtains the data set characteristics from the data set label (DSCB). If they are acceptable and the block size is larger, OPEN copies the block size to the DCB or DCBE.

For each JFCB or DSCB that this function of OPEN examines, OPEN turns off the DCB's standard bit, if the block size differs from the DCB or DCBE block size and the DCB has fixed standard.

If DCBBUFL, either from the DCB macro or the first DD statement, is nonzero, then that value will be an upper limit for BLKSIZE from another data set. No block size from a later DD statement or DSCB is used during OPEN if it is larger than that DCBBUFL value. OPEN ignores that larger block size on the assumption that you will turn on the unlike attributes bit later, will not read to that data set, or the data set does not actually have blocks that large.

   IEC034I INCONSISTENT RECORD FORMATS rrr AND iii,ddname+cccc,dsname