Delay Type

Reason

Wait for tape mount

A program or one of its subroutines is waiting for a tape mount.

Tape mount delays are experienced in the OPEN and End of Volume system services. End of volume processing is the function that requests subsequent volumes of a multivolume data set, which usually resides on tape.

Excessive OPEN and CLOSE requests for a file

A program or one of its subroutines might OPEN a file, perform a single I/O operation, and then immediately CLOSE the file. OPEN/CLOSE requests are very expensive operating system functions that contribute heavily to overall delay.

Small data set extent allocation

Additional time is spent allocating additional data set extents as the data set expands.

Reduce this type of delay by allocating a large enough data set to eliminate additional extent allocation.

High VSAM catalog activity

When a VSAM data set is OPENed or CLOSEd, a number of accesses are made to the CATALOG service routines to fetch control blocks or to write statistics.

It is not possible to control the time spent in CATALOG services, but files might be OPENed too often or unnecessarily.