StorageTek 6 manual Unavoidable Pass-Thrus, Unnecessary Pass-Thrus, Scheduled Pass-Thrus

Unavoidable Pass-Thrus

The HSC attempts to minimize the number of pass-thrus required; however, depending upon available tape transports and locations of cartridges, pass-thrus often cannot be avoided. By running Activities Reports on a regular basis and examining the results, you can see that mounts for different LSMs take longer than mounts for the same LSM.

Unnecessary Pass-Thrus

Scratch mounts, dismounts, enters, and ejects that require pass-thrus are unnecessary and should be avoided. These types of activities divert the robot from productive work especially during periods of peak activity.

If scratch subpools are properly defined and managed, scratch cartridges normally are not involved in pass-thrus. Scratch mounts are the same as specific mounts as far as pass-thrus that cannot be avoided. In general, you should never see a scratch pass-thru. But, if you do see a scratch pass-thru, it was unavoidable.

The effect of unnecessary pass-thrus is not obvious in the Activities Report. You must compare their number with average mount times to see the effect on performance.

Scheduled Pass-Thrus

Using the Scratch Redistribution utility to balance scratch cartridges involves moving cartridges to various LSMs to achieve scratch balancing. This type of activity involves heavy pass-thru usage. If you must balance scratch volumes across your library, schedule such activity during off peak hours. This approach will ensure that the pass-thru activity involved does not directly interfere with mounts and dismounts for high-priority production.

You can use Expert Library Manager (ExLM) to schedule pass-thrus. Refer to the Expert Library Manager User and Reference Guide for more information.

Ways to Reduce Pass-Thru Activity

There are various ways to reduce pass-thru activity. Each of these ways is briefly discussed in the following paragraphs.

Set MNTD Float to ON

The Float option of the MNTD command specifies whether the HSC is to select a new home cell location when it dismounts a volume that requires a pass-thru when it is dismounted.

When MNTD Float is set to ON, cartridges are not passed back to their original LSM. The cartridges are assigned new cells in the LSM where they are dismounted. This action eliminates most unnecessary pass-thrus.

Set MNTD SCRDISM to CURRENT

When MNTD SCRDISM is set to CURRENT, scratch cartridges mounted in a 9360 (WolfCreek) LSM are dismounted in the same device rather than being archived in the next largest storage device.

Chapter 6. Performance Considerations 423

1st ed., 6/30/04 - 312579601