Improved cache management enables you, through your installation's ACS routines, to select a cache preference group of 0 or 1. You can use the storage class initial access response time (IART) parameter at the host to select the preference group. If the value specified in this parameter is greater than or equal to 100, the logical volume is associated with cache preference group 0. If the value specified is less than 100, the logical volume is associated with cache preference group 1, which is also the default. When space is needed in the cache, logical volumes associated with preference group 0 will be removed from the cache before logical volumes associated with preference group 1. Volumes are removed from preference group 0 are based on their size, with the largest volumes being removed first. Volumes continue to be removed from preference group 1 based on a least recently used algorithm. Data written to the VTS for backup or long-term archival purposes can assign a storage class that specifies an initial access response time parameter greater than or equal to 100.

With outboard policy management support, you can define the cache preference level at the library through the library manager storage class policy, rather than through the IART parameter. The outboard specification overrides the host IART specification if you have defined a cache preference level setting in the library manager policy construct definition. If the outboard construct was automatically created and was defined with no cache specification, the host IART specification is used. If there is no IART specification, then the default preference level of 1 is used for the volume.

Starting with Release 1.6 of the TS7700 Virtualization Engine, you can use the LIBRARY REQUEST command at the host to temporarily override (while the volume is in cache) a volume’s preference group assignment, causing the volume to remain in cache longer or to be removed from cache sooner. Refer to Requesting information from the TS7700 Virtualization Engine for information on the LIBRARY REQUEST command. For additional information on this enhancement and other cache management-related removal options, refer to the TS7700 Customer Information Center.