Disk and tape devices

For optimal performance, use disk devices to which little other activity is directed, for work data sets. Specify high-speed devices such as IBM's TotalStorage DS8000 storage subsystems, and avoid specifying tape or virtual (VIO).

Using tape devices for work data sets rather than disk causes significant performance degradation for the following reasons:

Tape work data sets prevent DFSORT from using its more efficient sorting techniques, Blockset and Peerage/Vale. Disk work data sets allow DFSORT to use these techniques.
Tape work data sets must be accessed sequentially. Disk data sets can be accessed randomly.
Disk control units can provide additional features, such as cache fast write, that are not available with tape devices.