Data classes help to automate the allocation of tape mount management candidates on the DASD buffer. During your initial implementation of tape mount management, you can supply space information directly for tape data sets that are allocated without using the SPACE parameter. SMS data classes can specify this space without changing JCL.

Data classes can also be used as artificial classes, or flags, in your ACS routines to determine the data category that the tape data set belongs to, and whether to system manage it. You can set these artificial classes in the data class ACS routine, and check them in the storage class ACS routine when you determine if the data set is to be system-managed.

In general, tape mount management data sets do not have special performance or availability requirements, so new storage classes are not required. After you gain experience with tape mount management implementation, evaluate whether some candidates might benefit from sequential data striping.

The TMMBKUP and TMMACTV management classes support the two major categories of tape mount management data. TMMBKUP data moves to migration level 2 directly. TMMACTV data resides in the DASD buffer and migrates normally through the storage hierarchy, based on frequency of use.

Define new storage groups to support tape mount management data.

Recommendation: Define at least one separate storage group for the DASD buffer, because the threshold management policy for this set of volumes differs from others. Set the low threshold based on the space requirements for new tape mount management data allocations during periods of peak tape usage. Set the high threshold so a full cartridge of data, at least, is written during interval migration.

Consider setting up an overflow storage group of volumes (also known as a "spill" storage group). An overflow storage group serves as a reserve area for primary space allocations during periods of high space utilization in your pool storage groups. You can designate an overflow storage group in ISMF using the Pool Storage Group Define Panel. Assign designated overflow storage groups in your storage group ACS routine to make them eligible for allocations.

During volume selection, volumes in an overflow storage group are less preferred than those in an enabled storage group but more preferred than those in a quiesced storage group.

Exception: When an overflow storage group contains more volumes than a buffer storage group, specified volume counts might result in volumes in the overflow storage group being preferred over volumes in the buffer storage group.

Table 1 summarizes the types of data sets, tape mount management technique, and their corresponding SMS classes and groups.