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30 Storage Management with DB2 for OS/390
determined by either the Management Class for SMS managed data
sets, or set by the ADDVOL parameter for HSM managed. It can also be
controlled in combination with volume thresholds set by the storage
administrator. Data sets may be migrated to ML1 (normally disk)
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,after
a period of inactivity, and then onto ML2 (tape) following a further period
of non-usage. It is feasible, and maybe more appropriate in certain
cases, to migrate directly to ML2. Additionally, there is an interval
migration process which can be used to free space on volumes during
times of high activity.
• Expiration processing
This is based upon the inactivity of data sets. For HSM managed
volumes, all data sets are treated in the same way on each volume. For
SMS managed volumes, the expiration of a data set is determined by
the Management Class attributes for that data set.
• Release of unused space
HSM can release over-allocated space of a data set for both SMS managed and
non-SMS managed data sets.
• Recall
There are two types of recall:
• Automatically retrieving a data set when a user or task attempts to access
it
• When the HRECALL command is issued
All recalls are filtered; if the data set is SMS managed, then SMS controls the
volume selection. If the data set is non-SMS, HSM directs the volume
allocation. However, it is possible for the storage administrator to control a
recall and place it on an appropriate volume or Storage Group if required.
4.3.3.2 Availability Management
The purpose of availability management is to provide backup copies of data sets
for recovery scenarios. HSM can then restore the volumes and recover the data
sets when they are needed.
• Incremental backups
This is the process of taking a copy of a data set, depending upon whether it
has changed (open for output; browse is not sufficient), since its last backup.
For SMS managed volumes, HSM performs the backup according to the
attributes of the Management Class of the individual data set. For non-SMS
managed volumes, HSM performs the backup according to the ADDVOL
definition.
• Full volume dumps
A full volume dump backs up all data sets on a given volume, by invoking
DSS. HSM Dump Classes exist which describe how often the process is
activated, for example, daily, weekly, monthly, quarterly or annually.
• Aggregate backup
ABARS is the process of backing up user defined groups of data sets that are
business critical, to enable recovery should a scenario arise.
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Very large data sets, in excess of 64,000 tracks, cannot be migrated to disk: they must be migrated to migration level 2 tape.