On 9/1/2013 6:47 AM, Tom Russell wrote:
In the case of multiple steps each allocating one file on the same tape, and no AFF parameter used, there was (is?) a significant difference between JES2 and JES3.

JES2 would allocate as many tapes as there were steps, and rewind an unload the volume after each step and issue a mount for the same volume on the next tape drive. JES3 had Tape High-Water Setup, and would allocate a single tape unit for the volume, and not rewind and unload it between steps.

The only fix for JES2 was to add UNIT=AFF and DISP=(,PASS) to the JCL. JES3 didn't mind that you left them out.

I can't test this as I have no JES3 system.

Yes, It magically behaves almost as if JES3 under the covers issues an MVS MOUNT command for the tape volume and then later issues the MVS UNLOAD command at exactly the right time.

--
Edward E Jaffe
Phoenix Software International, Inc
831 Parkview Drive North
El Segundo, CA 90245
http://www.phoenixsoftware.com/

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