The sharing you want to do is ONLY supported with the single-host
configuration, ie.  two adsm instances on one box as your two servers.  The
scsi standard for dual-porting the drives to two different hosts is not yet
supported in the drive microcode.  That is why it is very important that one
drive NOT be available to two systems at the same time.

On the same host, however, it's a different story.   ADSM does tolerate two
applications, eg. two adsm servers, sharing the 3494 drives, but "tolerate" is
a better word than "support"  IMHO.  The main problem is controlling the
contention for the set of drives.   When server A finishes with the first tape
in a series, and dismounts it, server B is free to grab the drive.   When
server A proceeds to mount the second tape, it has to now wait for server B to
finish.   When it does, A grabs it and now B has to wait.   Sort of  like a
like a dove-tailed joint for you wood-workers.

You'll have to make any adjustments based on your schedules, etc, but here is
what I would recommend:

1) set the mountwait limit rather high-  This is how long server A will wait
for server B to finish before A will give up.  The default 60 minutes may be
insufficient, but keep in mind that the user on the client-end will be waiting
for this duration.

2) set the mountretention low-  the time server A will be waiting for B to
finish includes B's idlewait time.  The feature that causes idle mounts to be
dismounted to make room for new mounts does NOT span servers.

3) don't share all 8 drives, but set the mountlimit to something like 4 to 6
(and not the new default "DRIVES")-  This is because A does not have to wait
for the same drive that B has grabbed, any open drive will do.  By not sharing
all 8 drives, you'll lower the contention by keeping  a few mount points free
to service A when it needs the second tape.

I've been making these recommendations for some time, but have not heard much
from customers who are doing it and how they find sharing to work.   I would
like to see posts here as to what results they have :-)

Craig Bell