To balance the workload across the two enterprise tape control units, the virtual tape devices should be divided equally across the controllers. For example, if the size of the disk repository supports fewer than 256 devices (for example 128 devices), define 64 devices using subsystems X'01' through X'04' and 64 devices using subsystems X'11' through X'14'. Or, if a given host only needs a subset of the devices, spread the online devices in equal proportions across the two enterprise control units.

If an imbalance across the two enterprise tape controllers is observed with one enterprise tape controller (and its tape subsystems) getting the majority of the mounts, consider using the new MVS Device Allocation TAPELIB_PREF randomization option "BYDEVICES". For a discussion of the load balancing option, refer to Load balancing considerations.

For additional information on the IBM System Storage TS7680, refer to the TS7680 Information Center and APAR OA27786 (z/OS V1R9 and above).