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# Control Area Size Calculation for Striped VSAM Datasets

IP.com Disclosure Number: IPCOM000014683D
Original Publication Date: 2000-Jan-01
Included in the Prior Art Database: 2003-Jun-20
Document File: 2 page(s) / 30K

IBM

## Abstract

An algorithm that calculates control area sizes for striped VSAM datasets is disclosed. Problem: Control Area (CA) calculation for striped VSAM data set must be a integral multiple of the stripe count for striped VSAM data sets. Discussion: CA calculation for VSAM data sets has always been a factor of DASD space allocation. All allocation units (kilobytes, megabytes, and blocks) except cylinders are converted to tracks for CA calculation. An extend must be in whole CAs; therefore, the CA amount must be the lesser of the primary and secondary allocation amounts. If the allocation amount is cylinders, or the converted track amount for both primary and secondary allocation would result in a cylinder allocation for both primary and secondary allocation, the CA size is one (1) cylinder. Historically, 1 cylinder has been 15 tracks. This means that CA size has never exceeded 15 tracks to date. Striped VSAM data sets put two new requirements on the CA calculation algorithm: 1) the CA size must be an integral multiple of the number of stripes, and 2) a striped VSAM data set can have a maximum number of 16 stripes. The first requirement makes it necessary to change the initial allocation units since the CA size must be an integral mutiple of the number of stripes. The second requirement allows for a CA size of at least 16 tracks to provide for a data set with 16 stripes.

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Control Area Size Calculation for Striped VSAM Datasets

An algorithm that calculates control area sizes for striped VSAM
datasets is disclosed.

Problem: Control Area (CA) calculation for striped VSAM data set
must be a integral multiple of the stripe count for striped VSAM data sets.

Discussion: CA calculation for VSAM data sets has always been a factor
of DASD space allocation. All allocation units (kilobytes, megabytes, and
blocks) except cylinders are converted to tracks for CA calculation. An extend
must be in whole CAs; therefore, the CA amount must be the lesser of the
primary and secondary allocation amounts. If the allocation amount is
cylinders, or the converted track amount for both primary and secondary
allocation would result in a cylinder allocation for both primary and
secondary allocation, the CA size is one (1) cylinder. Historically, 1
cylinder has been 15 tracks. This means that CA size has never exceeded 15
tracks to date.

Striped VSAM data sets put two new requirements on the CA calculation
algorithm: 1) the CA size must be an integral multiple of the number of
stripes, and 2) a striped VSAM data set can have a maximum number of 16
stripes. The first requirement makes it necessary to change the initial
allocation units since the CA size must be an integral mutiple of the number
of stripes. The second requirement allows for a CA size of at least 16 tracks
to provide for a data set with 16 stripes.

Solution: Several factors are taken in to account for striped VSAM data
set CA calculation; For simplicity, all calculations are done in tracks,
including cylinder allocations. An attempt is made to preserve the original
primary and secondary amounts when changing them to accomodate the stripe
multiple requirement. In order to preserve the traditional CA maximum of 15
tracks as closely as possible while recognizing the 16 track requirement for
striped VSAM data sets, only a maximum CA size of 16 tracks for a striped VSAM
data s...