2.6. Parameters affecting performance
The following VSAM parameters and options can affect performance.
2.6.1. Allocation units
When you define your new data set, either the end user or SMS administrator through defining a data class (DC) must specify the amount of space to be allocated for it. One of the allocation functions for a new data sets is the creation of the DSCB in the VTOC, is done by the DADSM routine. Refer to “Allocating a VSAM cluster” on page 31, for more information about allocation. If SMS is active, you can specify a data class and take advantage of the space allocation set by your storage administrator. If you choose to specify space explicitly, you can specify it for VSAM data sets in units of records, kilobytes, megabytes, ...