IBM Tivoli Storage Manager MOUNTLIMIT for Libraries with Mixed LTO Media
Abstract This tip provides information about setting the MOUNTLIMIT parameter with IBM Tivoli Storage Manager when using a mixed media Ultrium library.
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If you are using an IBM Ultrium tape library with both Ultrium 1 and Ultrium 2 drives (for example, the IBM TotalStorage UltraScalable Tape Library 3584), you need to carefully consider how to set the MOUNTLIMIT parameter when defining the IBM Tivoli Storage Manager device class (DEFINE DEVCLASS command). Because Ultrium 1 drives can read and write only Ultrium 1 media, whereas Ultrium 2 drives can read and write both Ultrium 1 and Ultrium 2 media, you want to optimize the use of the drives. For read or write tape mounts on an Ultrium 1 cartridge, IBM Tivoli Storage Manager will select an Ultrium 1 drive first if possible. If no Ultrium 1 devices are available, an available Ultrium 2 drive will be selected for the Ultrium 1 media. To prevent the case where all Ultrium 2 drives are loaded with Ultrium 1 media (leaving no drives available to read/write Ultrium 2 media), set the DEVCLASS parameter MOUNTLIMIT appropriately, for example: MOUNTLIMIT can be set to the number of Ultrium 1 drives in the library for the Ultrium 1 devclass, so it will not use Ultrium 2 drives at all. MOUNTLIMIT can be set to the number of Ultrium 1 drives plus half the number of Ultrium 2 drives. This is a compromise position to allow good drive utilization, but reserve some Ultrium 2 drives for Ultrium 2 media.
You should experiment to define a suitable MOUNTLIMIT that works for your environment.