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Determining the Number of Static Cache DASD Volumes

The effective capacity for the various DASD device types is less than the total DASD device capacity. What follows is a breakdown for each device type, for the 400, 800, and 2000 MB Virtual Volume sizes. Assumptions for all of the device types are that the devices contain no other data, and that two cylinders contain the VTOC, VTOC Index, and the VVDS.

To calculate the number of DASD volumes needed for the forecasted DASD buffer (cache), use the following formula:

(DASD buffer size * 1000 / LDS size) / LDSs per Volume

The LDS size for 400 MB Virtual Volumes is 40 MBs. The LDS size for 800 MB Virtual Volumes is 80 MBs. The LDS size for 2000 MB Virtual Volumes is 200 MBs.

The following table lists LDSs per volume for 400 MB Virtual Volumes. Each LDS will use 854 tracks:

The following table lists LDSs per volume for 800 MB Virtual Volumes. Each LDS will use 1707 tracks:

The following table lists LDSs per volume for 2000 MB Virtual Volumes. Each LDS will use 4267 tracks:

For example, a 100-GB DASD buffer with 400-MB Virtual Volumes allocated on 3390-3 devices would generate the following formula and answer:

(100 * 1000 / 40) / 58 = 43.1 (rounded to 44)

A total of 44 3390-3 DASD volumes would be required.