Private volumes

Memory management is the responsibility of the user. The user can avoid access conflicts in the case of files which are used regularly by specifying the exact location of the files in the relevant volumes.

The number of management I/Os in the case of file processing calls with catalog access is considerably higher than with public volumes owing to additional accesses to the VTOC (Volume Table Of Contents) area. There are, for instance, 6 logical accesses to the F1 labels per OPEN/CLOSE pair, each of which requires one or more physical I/Os.

Thus efficient performance behavior can only be achieved if the number of management I/Os is small compared with the number of “productive” I/Os.