Explanation: SMALLDATASETPACKING | NOSMALLDATASETPACKING are mutually exclusive, optional parameters specifying whether
or not to pack small data sets into predefined VSAM key-sequenced
small-data-set-packing data sets on migration level 1 volumes.
SMALLDATASETPACKING specifies that when a small data set migrates,
it is eligible to be packed into a predefined VSAM key-sequenced small-data-set-packing
data set on a migration level 1 volume.
For tracks, substitute a decimal number from 1 to 18 specifying
that DFSMShsm consider any data set using that number of tracks or
fewer as a candidate for migration to a small-data-set-packing data
set. DFSMShsm converts the tracks value to kilobytes with
an assumed track size of device type 3380.
KB(kilobytes) specifies the source size of a data set
to be considered as a candidate for migration to a small-data-set-packing
data set. For kilobytes, substitute a decimal number from
1 to 800.
The source size of a DFSMShsm data set is calculated by multiplying
the number of bytes per track for the device type times the number
of tracks used by the data set. This calculated value is compared
to the value specified in the SMALLDATASETPACKING parameter. If the
calculated value is equal to or less than the value specified in the
SMALLDATASETPACKING parameter, the data set is a candidate to be migrated
to an SDSP. A candidate data set is eligible for migration to an SDSP
data set if its estimated size, after compaction, is less than or
equal to 400 kilobytes or to the value you specify, whichever is smaller.
The number of bytes per track for each DFSMShsm device type is as
follows:
- 3380 is 47,476 bytes per track
- 3390 is 56,664 bytes per track
The compaction size of a DFSMShsm data set is determined in one
of two ways:
- If compaction during migration is not active, the source size
equals the migration size.
- If compaction for migration is active, an internal default of
50% is used in establishing the estimated compaction size for data
sets that are candidates for an SDSP. Previous compaction history
is not considered for determining SDSP candidacy.
NOSMALLDATASETPACKING specifies that when small data sets migrate,
they are not packed into predefined VSAM key-sequenced small-data-set-packing
data sets on a level 1 volume, even if you specified the MIGRATION(SMALLDATASETPACKING)
parameter of the ADDVOL command for the volume DFSMShsm selects.
SMS relationship: Parameter has the same
meaning when applied to SMS-managed or non-SMS-managed DASD volumes
or data sets.
SETSYS default: None.
DFSMShsm default: If you do not specify tracks or KB(kilobytes) with the SMALLDATASETPACKING parameter
on any SETSYS command, the DFSMShsm default is 120 KB.
If you do not specify either SMALLDATASETPACKING or NOSMALLDATASETPACKING,
the DFSMShsm default is NOSMALLDATASETPACKING.
Note: - This parameter applies only to data sets that migrate from primary
volumes to migration level 1 volumes.
- If both tracks and kilobytes are specified,
only the kilobyte value is honored.
- Small-data-set-packing data sets have the following advantages:
- The volume table of contents of the migration level 1 volumes
are not filled with DSCBs for small data sets.
- Small data sets become records in the small-data-set-packing data
sets, so they do not have to start on track boundaries, giving you
a better use of space on the migration level 1 volumes.
- You get reduced volume fragmentation on the migration level 1
volumes.
- Specify both primary and secondary extents for the small-data-set-packing
data sets. If you want to use small data set packing, you should specify
the SMALLDATASETPACKING parameter of the ADDVOL command for at least
one migration level 1 volume per migration task. You do not have to
specify SMALLDATASETPACKING for all migration level 1 volumes. If
a data set is eligible for small data set packing, DFSMShsm selects
a volume that has been added to DFSMShsm with the SMALLDATASETPACKING
parameter.
- The names of small-data-set-packing data sets have the following
format:
uid.SMALLDS.Vvolser
DFSMShsm replaces uid with the UID you specified in the DFSMShsm
startup procedure.