Storage group-defined data sets
For a storage group-defined space, when NGT Recover defines the underlying data set, NGT Recover uses the following algorithm:
Obtain volume information for the storage group definition from SYSIBM.SYSVOLUMES in the DB2 system catalog.
If the data set is currently cataloged, obtain the volume information from the operating system catalog entry. Arrange to favor those volumes if they are still part of the STOGROUP definition.
Determine whether the data set is SMS managed by calling IGWAQSMS (DFP 3.2) or IGWASYS (DFP 3.3 or later).
If the data set exists, delete it (unless REDEFINE NO is specified). If it is not on the volume indicated by the operating system catalog entry, delete the data set with the NOSCRATCH option of IDCAMS. If REDEFINE YES NOSCRATCH is specified, no attempt to scratch the data set is made; it is simply uncataloged with the NOSCRATCH option of IDCAMS.
Define the data set. The following pseudo code shows which volume is selected for the initial definition of the data set and any subsequent extend requests that require a new volume. If a define or extend request fails, NGT Recover tries the algorithm again. Volumes on which an extend request fails are internally marked as tried.
IF THE STOGROUP DEFINITION INCLUDES SPECIFIC VOLSERS AND ANY VOLSER UNTRIED *DEFINE/EXTEND USING THE NEXT UNTRIED VOLSER ELSE IF THE STOGROUP DEFINITION INCLUDES '*' AND THE DATA SET IS SMS MANAGED DEFINE/EXTEND USING '*' ELSE DEFINE/EXTEND USING AN ORIGINAL VOLSER THAT IS UNTRIED
Specific volume serial numbers are used in the order in which they are returned by SQL from SYSIBM.SYSVOLUMES. For more information about how to change the volume ordering, please see the discussion of the STOGROUP USEORDER option in STOGROUP specification description.
If a nonpartitioned space is in multiple data sets, unused data sets are removed even with the REDEFINE option set to NO.
If the extend request requires a new data set or volume, it will be defined even with the REDEFINE option set to NO.
If an Instant Snapshot copy is used to recover the object, REDEFINE YES has no effect and the data sets are processed as if REDEFINE NO had been specified.
Primary space allocation
If the PRIQTY value is specified, it is used for primary space allocation. If PRIQTY is not specified, the DSNZPARM TSQTY value is used. If TSQTY is set to 0, then 1 cylinder is the default primary space allocation.
The SECQTY value is used for secondary extents if DSNZPARM MGEXTSZ is set to NO. If MGEXTSZ is set to YES or SECQTY is not specified, NGT Recover uses a sliding-scale calculation for secondary extents, similar to the method DB2 uses.
For more information about the sliding-scale calculation, see the IBM DB2 for z/OS SQL Reference.