Defining management class migration attributes

To DFSMShsm, a data set occupies one of two distinct states in storage:

Primary: Also known as level 0, the primary state indicates that end users can directly access a data set residing on a volume.
Migrated: End users cannot directly access data sets that have migrated from the primary state to a migrated state. To be accessed, the data sets must be recalled to primary storage. A migrated data set can reside on either migration level 1 (usually permanently mounted DASD) or migration level 2 (usually tape).

A data set can move back and forth between these two states, and it can move from level 0 to migration level 2 (and back) without passing through migration level 1. Objects do not migrate. Movement back to level 0 is called recall.

Page 2 of the Management Class Define panel contains the management class migration and GDG management attributes. SCDS Name and Management Class Name are output fields that contain the SCDS and management class names you specified in the Management Class Application Selection panel.

To define a management class, you must specify values for the Partial Release and Command or Auto Migrate attributes. If you specify BOTH for the Command or Auto Migrate attribute, then Primary Days Non-usage and Level 1 Days Non-usage become required fields. If you specify NONE for the Command or Auto Migrate attribute, the expiration attributes specified on page 1 of this panel still apply. The other fields on this panel are optional.

Partial Release Attribute

Applies to non-VSAM data sets and to all VSAM data set types allocated in the extended format. You can use partial release to choose the conditions under which unused allocated space is released. If you select partial release, space release is carried out automatically at the time you have selected. Each partial release option releases the same amount of space. Unused space is released in cylinders or tracks, depending on the space allocation unit used. The following options are available for partial release:

Y: Yes. Release unused space at Space Management cycle time.
YI: Yes Immediate. Release unused space at Space Management cycle time, when close is issued for a data set that was open for output, and on subsequent volumes.
C: Conditional. If a nonzero secondary space allocation has been specified for the data set, release unused space at Space Management cycle time. This option only applies to physical sequential and partitioned data sets. If specified for an extended format VSAM data set, this option is processed as if Yes were specified.
CI: Conditional Immediate. If secondary space has been allocated, release unused space at Space Management cycle time, when close is issued for a data set that was open for output, and on subsequent volumes.
N: No. No release of unused space.

Note:

ISMF primes the field with the last used value. The default is N.
The Partial Release attribute is not checked during DFSMShsm interval migration.
The Partial Release attribute is mutually exclusive with the Guaranteed Space storage class attribute.
Partial release is ignored under the following conditions:
- Another job is sharing the data set (DISP=SHR).
- Another task in the same job is processing an OPEN, CLOSE, EOV, or FEOV request for the data set.
- Another DCB is open for the data set.

For more information on partial release, refer to z/OS DFSMS Using Data Sets.

Migration Attributes

Represents the minimum number of days that must elapse since last access before a data set is eligible for normal migration. Days refers to calendar days, not to a 24-hour time period. In other words, the day you close the data set counts as the first full day of nonusage. The minimum number of Primary Days Non-usage days required for migration to ML2 includes the time already spent unreferenced on ML0. The default is 2. (Refer to GDG Management Attributes, below, for the special GDS migration eligibility rules.)

A nonzero number for Level 1 Days Non-usage indicates the number of days that must elapse since the last reference on level 0 before a data set on ML1 can migrate from level 1 to level 2. The default is 60.

The Command or Auto Migrate attribute allows you to specify if a data set is eligible to be migrated by BOTH command and automatic processing, by command alone, or not at all (NONE).

If you do not want to migrate data sets that belong to a particular management class, specify NONE in the Command or Auto Migrate field. The data sets remain on primary storage until they expire. If you want data sets to be eligible for migration directly from level 0 storage to level 2 tape, specify 0 in the Level 1 Days Non-usage field. Otherwise, the data sets must first migrate to level 1 (the days spent on level 0 count toward the eligibility of moving to level 2).

GDG Management Attributes

Indicate criteria for early migration of GDGs off primary storage and what to do with rolled-off generation data sets (GDSs).

The # GDG Elements on Primary attribute indicates how many of the most recent generations of a GDG use the normal Primary Days Non-usage attribute for migration criteria. Generations that are over this limit are eligible for early migration during the next processing of primary space management. The inactive age is irrelevant for these 'over the limit' GDSs and they are given a higher selection priority so they are likely to be migrated if space is needed to meet volume thresholds.

Tip: Specifying the # GDG Elements on Primary attribute does not ensure that the specified number of GDSs are kept on primary storage, but rather that their migration is not accelerated.

To specify that old generations are to have priority for migration and to specify how many generations are to have standard priority, you can specify the # GDG Elements on Primary attribute. When you specify this attribute, all non-rolled-off generations of each GDG that exceed the number you specify are given priority for early migration. If you specify 0 for this attribute, all generations of the GDGs are given priority for early migration. Those data sets made eligible for early migration do not have to satisfy the Primary Days Non-usage criteria.

All generations that meet the Primary Days Non-usage criteria are eligible to migrate. # GDG Elements on Primary enables you to accelerate migration of older generations while Primary Days Non-usage enables you to specify migration criteria of younger generations separately.

The Rolled-off GDS Action value indicates whether to expire rolled-off GDSs or to make them eligible for migration. If you specify MIGRATE, management class expiration attributes are applied to the data set to determine if the data set should be deleted; if not, the data set is eligible for migration. If you specify EXPIRE, the rolled-off GDS is deleted unless an explicit expiration date is in the DSCB. In this case, the rolled off GDS becomes a non-GDG data set and migrates according to non-GDG migration attributes.

Tip: The DFSMShsm parameter, EXPIREDDATASETS, controls the deletion of a data set with an expiration date in the DSCB.

Both the # GDG Elements on Primary and the Rolled-off GDS Action attributes are optional and have default values of blank. If left blank, no special treatment results from the data set being a GDS or a rolled-off GDS. That is, other management class attributes is used to process the data set.

During automatic primary space management, GDSs that have been determined as eligible for migration are migrated in the following priority order:

GDSs that are rolled-off.
GDSs that exceed the limit specified in # GDG Elements on Primary.
Other GDSs are handled by the non-GDG algorithm which bases priority on a function of size and the length of time it has been eligible to migrate in Primary Days Non-usage.

After specifying the migration attributes, issue the DOWN command to specify the backup attributes on the next page of the Management Class Define panel.