Not only the mountlimit for the deviceclass, but how many tape drives are
online versus how many are actually gen'd in the system via HCD. You may
have a string of 8-3590's gen'd, but currently only have 4 physically hooked
up. As far as MVS allocation is aware, these are devices that are just
offline. If TSM needs a tape drive, and there aren't any available, but
there are offline devices you end up with dynamic allocation messages from
TSM (can't remember the ANR* message) and/or the more familar REply Device
name, Wait, or Cancel message to the operator console. Message automation
can take care of some of this, but cancelling a request for a tape drive to
TSM can fail a backup or process. This is probably the thing I hate the most
about TSM on OS/390...you can't tell TSM EXACTLY how many drives are
available. All allocation goes through OS/390.

Bill Boyer
DSS, Inc.