Tape Mounts on VM Server -Reply

FYI:  We have been running ADSM on VM for about 18 months.  We spent a few hours
setting up the tape exit machines and execs during installation and we have had
   no
tape problems.  The tape management system is VMTAPE.  However, I did define 1 e
   xit
machine for each real tape drive (6) plus a couple of extras for asynchronous
scratch requests (for a total of 8).  Extra exit machines cost nothing, they can
share the same minidisk or directory.

Dennis Taylor
Georgetown University Hospital

>>> Greg Piney <zzgcp AT MCGRAW-HILL DOT COM> 03/15/95 02:17pm >>>
   Unlike other operating systems, VM still uses an antiquated method for mounti
   ng
tapes. Some vendors have improved this with the help of a service machine. Other
   s
have systems which allow VM systems to share tape drives with MVS. In my case, w
   e
use both.
   When the VM ADSM server needs a tape, he autologs the tapemount exit machine.
    It
is the job of this machine to acquire a drive, check the mounted volume, and the
   n
give the unit to DSMSERV. In the vanilla environment, this probably works well.
   In
our case, the exit machine issues a VMTAPE (Sterling Software) 'Mount' command f
   or
the tape and waits for the mount to complete. VMTAPE processing calls MIA/VM
(Legent) acquires a unit from the pool shared with
MVS. Once the drive is acquired, VMTAPE then calls for the requested volume. Onc
   e
the correct volume and mode has been checked, VMTAPE hands over the unit to DSMS
   ERV
and command completion occurs on the exit machine. Once command completion occur
   s
on the exit machine, I check the return code from VMTAPE and additionally check
that the mount was successful (vcuu is attached to DSMSERV).
This processing takes from 1-10 minutes. Normally this is fine.
Since the beginning, the server would occasionally mark the
Exit Machine 'Offline'. I thought it was MY problem and tweaked the Exit Machine
'Exec'. Recently It started occuring a bit more frequently.
   I have discovered that there are cases where the server has the need to mount
more than one tape. We only use one
Exit machine. The server will wait until the Mount is detected and then try to
autolog the service machine again for the next mount. If this process fails 3
times, the exit machine is marked 'Offline'. The server tries 3 times in less th
   an
1 second.
If the Exit Machine has not completed processing or logging off,
It is marked 'Offline'. This is unacceptable. Since the Server is using a REXX
based Exit Machine, a reasonable (or preferably selectable) period of time elaps
   e
BEFORE the Server attempts to autolog the exit machine again. This time period
should elapse BEFORE each attempt at autologging. This would allow any
Post-Mount processing in the exit machine to complete and Logoff.
I have been reduced to constantly monitoring the ADSM server to make sure
everything is fine.

    I NEED A FIX AND I NEED IT NOW!!!

   I also need a mechanism to tell the ADSM server 'Sorry, No
Tape Drives available now, Try again later.'.


TIA,

Greg Piney
Sr. Systems Engineer
McGraw-Hill Inc.