Summarizing direct access volume activity

SMF reports information about problem-program use of direct access volumes. The examples that follow show how operations personnel can use this SMF information to examine problem-program use of direct access storage.

Allocated but unused direct access storage

There are many times when users make allocation requests for direct access storage that exceed the actual requirement. This misuse can be a significant drain on the direct access resource pool. To determine the number of tracks allocated for sequential data sets but not used, an installation can compare the following two fields in the SMF type 15 records:

The relative track of the last record written in the DASD extension of the DCB/DEB section
The total number of tracks allocated in the DASD extension of the UCB section

Volume mounting

SMF writes a type 19 record whenever a volume that is defined by a DD statement is demounted. Summarizing these records by volume can give an installation some indication of its direct access volume mounting activity for problem programs.

In addition, an installation can use the SMF type 25 records to summarize the JES3 volume mounting for problem programs. JES3 produces a type 25 record for each job that main device scheduling (MDS) processes. These records show both the number of tape volumes and the number of disk volumes mounted for a job.

Fragmented volumes

Periodic analysis of the SMF type 19 records can be useful in identifying direct access volumes whose unallocated space is fragmented. An installation can identify the volumes that might need reorganization by examining the relationship of the following SMF fields:

The number of unallocated cylinders and tracks
The number of cylinders and tracks in the largest unallocated extent
The number of unallocated extents

An installation can further analyze the unallocated space on direct access volumes by comparing the number of unallocated tracks with the number of available data set control blocks (DSCB). For example, such a comparison might show that even though a given volume still has 50 free tracks, its amount of additional space is limited because there is only one available DSCB.