DFSMShsm small-data-set-packing data set facility

The small-data-set-packing (SDSP) data set facility of DFSMShsm allows DFSMShsm to migrate small user data sets from level-0 volumes and to store them as records on level-1 migration volumes where the records of several data sets can share the same track. Small user data sets are stored in SDSP data sets on level-1 migration volumes.

If a data set is eligible to be migrated to an SDSP data set, DFSMShsm selects a migration level-1 volume containing a non-full SDSP data set. If no migration level-1 volumes contain a usable SDSP data set, the data set migrates as a separate data set. If the data set is ineligible for migration to an SDSP data set, it migrates as a data set. SDSP data sets are allocated only on migration level-1 volumes. Each migration level-1 volume can contain only one SDSP data set.

Figure 1 illustrates how small-data-set-packing data sets save space on level-1 migration volumes. SDSP data sets offer the following advantages:

Reduced fragmentation of a level-1 volume.
Reduced use of space in the volume table of contents (VTOC). Because the small-user data sets are stored as records, migration level-1 VTOCs are not filled with an entry for each small user data set that resides in an SDSP.
Better use of space on the migration level-1 volumes. Small data sets become records in the SDSP data sets and, as such, share the same tracks.

	Small-Data-Set-Packing Data Sets
	Required: No. Allocated by starter set: Yes, see ALLOSDSP. Maximum record size: 2093 bytes. Data set type: VSAM key-sequenced data set (KSDS) on level-1 migration volume. Storage guidance: SDSP data sets must reside on level-1 DASD migration volumes, and each must have a specific name. Allocate only one SDSP data set per level-1 migration volume.