ESS 2105-F20 OS/390 allocations are usually done in increments of multiple logical 3390-3s (3,339 CYL each). For example, using 18GB DDMs, you can allocate 36 logical volumes, RAID-5 protected, within an eight pack (six storage DDMs, one spare DDM, and one parity DDM). This leaves 2,034 CYL unused, but it can still be allocated as a custom volume 3390-3. This smaller custom volume can be used within SMS as a temporary pool volume. Sort files and &&temp files work well on these special volumes with no backup required. Therefore, you don't have to worry about disaster recovery for these files. By doing this, you can free up one 3390-3 volume from the temporary pool for more important uses of storing critical data from every eight pack array.
No matter what size DDMs you are using for OS/390 allocations, you should always check for unused space within each array. The ESS Specialist will display this information for you. Therefore, no space will go unused.
About the author: Dex Watson has been a member of the IT community since 1967. He has extensive hands-on knowledge of storage hardware and software. As the enterprise storage manager of Utica National Insurance Group, his responsiblity covers three platforms: OS/390, AIX and NT.