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Chapter 6. Performance Considerations 425
1st ed., 6/30/04 - 312579601
Prefetch Enters
Nonlibrary cartridges that are mounted on library transports are delayed while the
operator fetches and enters them. This is a common occurrence for HSC sites with all
transports attached to the library.
If you or your scheduling system can predict which nonlibrary cartridges will be
mounted in the library before a mount message appears, your operator can improve
performance by entering those cartridges in advance.
Avoid Crashing Test Systems
Library attached hosts own library resources, including CAPs, tape drives, and
cartridges. If a host fails, another host must clean up the resources held by the failing
host. This delays mounts and dismounts on the recovering host while recovery takes
place.
You should attempt to shut down the HSC properly before IPLing a system. This is
especially important for test systems that may be restarted several times a day.
Reduce Tape Transport Contention
Balanced use of library tape transports results in better robotic and system
performance. In a multiple LSM library, you want the workload to be spread evenly
among the robots rather than having one robot overloaded while the others are idle.
Within each LSM, you want mounts to be evenly distributed among transports rather
than having the robot wait for a cartridge to be rewound so it can mount the next
cartridge on the same tape transport.
Tape transport contention can be reduced by:
• ensuring scratch cartridge balance
• managing multi-host tape transports
• avoiding dedicating tape transports
ACSPROP EXEC
Utility ACSPROP EXEC is provided for use as a programmable operator (PROP) action
routine to process all
TAPE raddr DETACHED...
messages which CP sends to the system console.
It issues library DISMount commands for the given tape drive (raddr). The dismount is
honored if the HSC did a mount to that device for the same host. VM (CP) causes a
‘Rewind Unload’ command to be executed on any tape drive DETACHed by the CP
commands LOGOFF, FORCE, or DETACH. This would leave a library volume in a
‘selected’ state physically sitting in a library transport. The volume is unavailable to any
requestor until it is removed from the drive and placed back in a storage cell of an LSM.
ACSPROP EXEC is an ‘‘action routine’’ which may be invoked by the VM
PRogrammable OPerator service to issue HSC DISMount commands when a tape drive is