Like so many of the things IBM does, it is a left over from when we had several different DASD types going all the way back to OS/MVT/MFT days... 3120 was optimum for any...
But today, for the most part, BLKSIZE=0 is OK and the OS will calculate the proper size for the device you are writing on. That, could be a multiple of 64K or 256K for tape ( if you have large block enabled ) or generally 1/2 track multiple for 3390, like 27920 for LRECL 80. It is important to remember that there are other factors, like HARD CODING a BLKSIZE in an application, like COBOL ... BLOCK CONTAINS 10 RECORDS ... instead of BLOCK CONTAINS 0 RECORDS ... which would require a specific BLKSIZE or MAXIMUM BLKSIZE. 3390's have a track size of ... 56664 ... but DASD has a 1/2 track limit on the BLKSIZE ( probably has something to do with 32767 and a historical artifact ) Using a large BLKSIZE when writing the XMIT file has NOTHING to do with JES(2/3) .... Regardless of the BLKSIZE, with JES(2/3) they process the 80 byte records ( CARD IMAGES ) as a PSEUDO device ... SYSIN / SYSOUT type ... If the DASD SET is large ( TERSE PACK ) before XMIT would save space ... Paul ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
