There are occasions where the DASD environment for a Restore/Recover has become so fragmented that there is not enough space to satisfy the request for storage because z/OS is unable to acquire the space requested in five extents or less on one volume, even though the space may be available in multiple extents or across volumes. This causes the Restore to fail and requires human intervention to resolve the space shortage.
Traditionally CA Disk has attempted to work around this by requesting a smaller amount of storage, either the original primary amount or the sum of the first three extents, and relying on secondary extents to fill the amount needed. However this sometimes failed due to various other environmental causes. CA Disk now uses a facility provided by z/OS that was introduced called Space Constraint Relief. This allows CA Disk to request that z/OS allocate the data set and relax some of the constraints that it works under.
In particular, z/OS will allocate the data set with more than five extents – up to the maximum extents the data set type supports – and can use multiple volumes to satisfy the request. The Space Constraint Relief is available under CA Disk only for SMS data sets, and the multiple volume support of Space Constraint Relief is available for SMS non-VSAM data sets regardless of number of volumes at the time of Backup/Archive and for SMS VSAM data sets that were contained on multiple volumes at the time of Backup/Archive.
A SYSPARM controls the multiple volume support of the Space Constraint Relief. The SYSPARM is SMSSCRVL, and it is a number from 0 to 59 which specifies the number of volumes that data sets can span if the data set is unable to be allocated using the number of volumes it originally occupied. The Bestfit facility is automatically invoked when normal Dynamic Allocation of a data set being restored, fails. An attempt is made to satisfy the request using the original number of volumes and, if that fails, an attempt is made to satisfy the request using the number of volumes specified by SMSSCRVL if it is greater than the original number of volumes.
Valid for RESTORE and RECOVER
This sysparm is the number of volumes that a data set can use if it fails normal allocation and a Bestfit attempt with the volumes originally allocated. It can be 1 to 59. This SYSPARM is only used for SMS non-VSAM data sets.