Physical sequential and VSAM data sets

The Sustained Data Rate (SDR) has an effect only for extended format data sets. Striping allows you to spread data across different DASD volumes and controllers. The number of stripes is the number of volumes on which the data set is initially allocated. Striped data sets must be system-managed and must be in an extended format.

When no volumes that use striping are available, the data set is allocated as nonstriped with EXT=P specified in the data class; the allocation fails if EXT=R is specified in the data class.

Physical sequential (PS) data sets cannot be extended if any of the stripes cannot be extended. For VSAM data sets, each stripe can be extended to an available candidate volume if extensions fail on the current volume.

If you do not specify Guaranteed Space=Y in the storage class, the following is true:

The system uses the SDR field in conjunction with the assumed device transfer rate to derive the number of stripes that a striped data set can have. The SDR field specifies the target throughput rate. Valid values for this attribute are blank or from 0 to 999. The maximum number of stripes for PS data sets is 59. For VSAM data sets, the maximum number of stripes is 16.
For nonguaranteed space requests, if the SDR field is blank or 0, the target number of stripes is 1. If the value in the SDR field is greater than 1, it is divided by 4 for 3390s, or by 3 for 3380s to determine the stripe count. For example, for an SDR value of 24, a storage group of 3380s would have a stripe count of 8, and a storage group of 3390s would have a stripe count of 6. The volume must be able to satisfy the requested primary space.
Depending on the number of eligible volumes in the candidate storage groups, the actual number of stripes allocated to a data set can be less than the derived one. As the stripe count is decreased, the primary space for each stripe increases, except for the guaranteed space requests.

If you specify Guaranteed Space = Y in the storage class, and for further information about guaranteed and nonguaranteed space allocation, see Rules for striping volume selection.

See z/OS DFSMS Using Data Sets for more information on using SMS to assign storage classes for striped data sets.