Step 6: Determine Whether There Is Enough Physical Space

When enrolling new file spaces in a file pool, you might consider checking the amount of physical DASD space available (unused) in the storage group. Use the QUERY FILEPOOL MINIDISK command and check the Storage Group Minidisk Information and Storage Group Minidisk Totals Information it displays. An alternative to QUERY FILEPOOL MINIDISK is the Query User Storage Group CSL Routine which can be used to check available storage group use. See QUERY FILEPOOL MINIDISK and z/VM: CMS Callable Services Reference for more about the Query User Storage Group CSL Routine.

There should be enough physical space to support the file space's initial set of files. For new z/VM® users, one can expect little file activity initially, so even a nominal amount of unused DASD space may be sufficient for a while. For existing z/VM users, you can expect more activity, especially if the user is moving existing files into the file pool. When the contents of a 191 minidisk is being moved to the file pool, the user might be able to tell you the number of 4KB blocks they will be immediately using. The storage group in which they are enrolled should have at least that many unused 4KB blocks.

After you have some experience with the rate at which users consume physical storage at your installation, it will become easier to decide whether the addition of a certain amount of users merits the addition of DASD space to the storage group to increase the file space. In any case, the file pool server displays a message on its console when the physical storage in a storage group is almost exhausted. At this point, you can add minidisks to the storage group, or move users to another storage group that has sufficient available space.

In general, it is a good policy to over-commit the storage group space. That is, it is good to assign more blocks to users than you actually have physical DASD space to support. This is particularly true if you are using DFSMS/VM to manage your storage. When infrequently used files are placed in DFSMS/VM migrated status, file blocks no longer reside in the storage group but are still counted in a user's file space usage. This lets you conserve your DASD space. Add DASD space only when necessary.