See UNIT=AFF
At 06:02 PM 1/10/2025, Farley, Peter wrote:
I have a business need to scan 15 different tape files (all the same
record format, some are multi-volume) to extract relevant
information, and I first tried to scan them all in one concatenated
DD. I didn't specify anything but DISP and DSN for each file in the
concatenation, so I got 15 tape mounts to 15 different tape drives.
I would like to limit the tape drive usage so as not to
unintentionally interfere with production work that actually needs a
tape drive. Using UNIT=AFF=INPUTDD on the second and all other DD's
in the concatenation limits usage to ONE tape drive, the one
allocated to the first file in the concatenation.
In order to reduce elapsed time for the scan job (each tape
dismount/mount operation takes an appreciable amount of time,
usually at least a minute or so), is there any way to use TWO drives
in one concatenated DD instead of one drive, so that as each file
reaches EOF the process continues with the already-mounted next file
while the system loads the EOF drive with the next file? If I knew
in advance the device numbers of tape drives that are actually
available I could try to use UNIT=device1 and UNIT=device2 on
alternating DD's, adding ",,DEFER" to all but the first two DD's,
but I don't know what drives are available before I submit the job.
If there is a way to use two drives without knowing the device
numbers ahead of time, what happens if one of the tape DD's is a
file that has multiple volumes? Does an already-mounted file from
the next DD get dismounted to load the next volume of the one being
processed, or does it dismount the first volume and wait for the
next volume to be mounted on the same drive?
These aren't "real" drives of course, they are all in a VTL, but the
principal is the same - don't occupy more devices than you really need.
Peter
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