Interval migration is a space management function that performs hourly space management on eligible volumes that
exceed specified volume threshold requirements. Interval migration
migrates data sets to ML1 or ML2 volumes and transitions
data sets from one class of user-accessible volumes to another until
the low threshold is reached or there are no eligible data sets remaining.
During interval migration:
- Information about the SMS configuration is obtained:
- A list of all volumes in all DFSMShsm-managed storage groups is
obtained.
- A list of active management classes is obtained.
- The percent of allocated space on each volume in the obtained
list is checked.
- A message is issued for unmatched data sets.
- Temporary data sets are deleted.
- Expired data sets are deleted.
- Data sets that are eligible for a class transition
are transitioned. If a data set is eligible for both a class transition
and migration, the data set will only be migrated. This prevents the
data set from being moved for a transition, only to be later migrated.
- Data sets that are eligible for migration are migrated.
The following functions that are performed during primary space
management are not performed during interval migration:
- Partial release.
- Extent reduction.
Specific interval migration eligibility requirements must be satisfied
both at the volume level and the data set level. See Interval migration eligibility requirements.
Enabling interval migration
Interval migration is enabled by default and there are two methods
of explicitly enabling interval migration:
- Add the SETSYS INTERVALMIGRATION command to the ARCCMDxx parmlib member of SYS1.PARMLIB. Then restart
DFSMShsm.
- Issue the SETSYS INTERVALMIGRATION command after DFSMShsm is started.
To determine if interval migration is enabled or disabled, issue
QUERY SETSYS. Message ARC0151I is issued with the query response.
To use interval migration after it is enabled, eligibility requirements
must be satisfied. See Interval migration eligibility requirements.
Disabling interval
migration
There are two methods of disabling interval migration:
- Add the SETSYS NOINTERVALMIGRATION command to the ARCCMDxx parmlib member of SYS1.PARMLIB. Then restart
DFSMShsm.
- Issue the SETSYS NOINTERVALMIGRATION command after DFSMShsm is
started.
Interval
migration eligibility requirements
There are two sets of requirements that must be satisfied in order
for a volume to be eligible for interval migration. The first set
of requirements must be satisfied at the volume level. The second
set of requirements must be satisfied at the data set level.
Requirements that must be satisfied at the
volume level
for interval migration to be performed are:
- The volume is either an SMS-managed or non-SMS-managed volume.
- The volume belongs to a storage group defined with AM=I (Auto
Migrate, interval) or AM=Y (Auto Migrate, yes).
- If the storage group is defined with AM=I, the volume must exceed
the midpoint between the low and high threshold to be eligible.
- If the storage group is defined with AM=Y, the volume must exceed
the high threshold to be eligible.
- If the storage group is defined with AM=Y, on-demand migration
must not be enabled for the volume to be eligible. Otherwise, on-demand
migration is performed.
- The SETSYS INTERVALMIGRATION setting is in effect.
Requirements that must be satisfied at the
data
set level for a data set to be
transitioned
or migrated from an eligible volume are:
- The management class for the data set is configured to allow both
command or auto migration (COMMAND OR AUTO MIGRATE=BOTH)
- - For transitions:
- The age of the data set has exceeded the management class TIME
SINCE CREATION attribute value.
- The last referenced date has met or exceeded the management class
TIME SINCE LAST USE attribute value.
- The current date has met or exceeded the PERIODIC time period
specified in the management class.
- For migration, the inactive age of the
data set has exceeded the management class PRIMARY DAYS NON-USAGE
attribute value.
- If the data set is a candidate to be backed up:
- It is not eligible for migration if the
migration of the data set is directed to tape.
- It is not eligible for a transition if the management
class TRANSITION COPY TECHNIQUE specifies a technique other than STANDARD.
Interval migration usage notes and other considerations
- Neither interval migration or on-demand migration is performed
on SMS-managed volumes that belong to a storage group defined with
AM=P (Auto Migrate, primary) or AM=N (Auto Migrate, no).
- Interval migration is performed on volumes that belong to storage
groups defined with AM=I regardless of whether interval migration
is enabled or disabled.
- When on-demand migration is enabled, on-demand migration is performed
instead of interval migration on eligible SMS-managed volumes that
belong to storage groups defined with AM=Y. For on-demand eligibility
requirements, see On-demand migration eligibility requirements.
- If you want to require operator permission before allowing interval
migration to run, issue the SETSYS REQUEST command.
- If you want the operator to be notified of the space allocation
of each volume during the interval migration space check, issue the
SETSYS MONITOR(SPACE) command.
- Data sets on SMS-managed volumes are processed
in the following order:
- Data sets eligible for a class transition and migration will be
migrated.
- Data sets eligible for a class transition will be transitioned.
- Data sets eligible for migration only will be migrated. For this
phase, data set size is a determining factor for the order and priority
in which data sets are migrated. The largest eligible data set migrates
first, followed by the next largest. The priority for migrating data
sets from volumes that belong to storage groups defined with AM=I
applies when the low threshold exceeds 5% only.
- In order for a data set to be migrated or transitioned by TIME SINCE LAST USE, the date of the current
backup copy should be greater than the date-last-referenced by at
least one day.
Related reading
- For more information about on-demand migration, see Using on-demand migration.
- For more information about the QUERY command and responses, see QUERY command: Displaying the status of parameters, statistics, and requests and Using the QUERY command.
- For more information about the SETSYS commands used, see SETSYS command: Establishing or changing the values of DFSMShsm control parameters.
- For a comparison of interval migration and tape mount management,
see Comparison of interval migration and tape mount management.
- For more information about managing storage and space requirements,
see Specifying the storage to be managed and the space requirements.
- For more information about exceptions for which management classes
are not included in the obtained list, see DFSMShsm retrieval of management classes and storage groups.
- For an illustrative event-driven migration scenario, see Event-driven migration example scenario.
- For other space management considerations, see Other space management considerations.
- For more information about space management of extended address
volumes, see Space management of extended address volumes (EAVs).
- For more information about storage groups and management classes,
see z/OS DFSMSdfp Storage Administration.