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I/O Facility Usage

The I/O Facility Usage report helps you analyze file access activity. It shows by device and volume, the percentage of run time used by the CPU to access each data set.

Report details

  • Unit number is the number assigned to the I/O device on which the active data set resides.

  • Device type is the type of device and its model number:

Type

Definition

(model number)

Direct access

TAPE

Magnetic tape

UR

Unit record

G

Graphic

C

Communication

  • Cylinder count is the number of cylinders defined for the device. This is displayed so users can differentiate between the various device types.

  • % of observed I/O with PAV/HPAV Displays the percentage of activity attributed to the device that occurred with allocated Parallel Access Volumes (PAVs). PAV indicates Static or WLM managed PAVS and HPAV indicates activity identified with HyperPavs. Note: PAVs that are defined with WLMPAV=YES will always be displayed as WLM managed. This field appears only if activity is observed.

  • PAV Type shows the PAV as either Static, WLM Managed, or HyperPAV.

  • Run time Total % shows the percentage of total run time that access to the unit, volume, or cylinder used, with or without concurrent CPU execution or other I/O activity.

Click next to the unit number to view additional detail:

  • Volume ID: the volume on which the data set is allocated.

  • DDNAME shows the data definition name of any active data sets.

  • Total: percentage of the total run time used to access the data sets, with or without concurrent CPU execution or other I/O activity.

  • Input %: percentage of total run time spent in input activity. Total: percentage with or without concurrent CPU execution or other I/O activity.

  • Output %: percentage of total run time spent in output activity. Total: percentage with or without concurrent CPU execution or other I/O activity.

  • Other %: percentage of total run time used to access unopened files.  Total: percentage with or without concurrent CPU execution or other I/O activity.

Click arrow next to the volume ID to view additional detail:

  • Cylinders shows the numbers of the cylinders on which the active data set resides.

  • VTOC location marks cylinder ranges that include a volume table of contents.

Analysis tips

  • If the report shows high access for index cylinders, sporadic access for data cylinders, or high access for one index cylinder, the file is probably being processed randomly. Examine the Data Set Characteristics  report to determine the block size and number of buffers allocated for the index portion of the file. Increasing the block size or number of buffers can improve performance.

  • If data cylinders show an even pattern of access, the file is probably being accessed sequentially. Examine the Data Set Characteristics report to determine if an increase in the block size or number of buffers allocated can help performance.