30 Storage Management with DB2 for OS/390
determined by either the Management Class forS MS managed data
sets,or set by the ADDVOL parameter for HSM managed. It can also be
controlled in combination with volumethresholds set by the storage
administrator.Data sets may be migrated to ML1 (normally disk)4,after
a period ofinactivity, and then onto ML2 (tape) followinga fur therperiod
of non-usage. Itis feasible, and maybe more appropriate in certain
cases, to migratedirectly to ML2. Additionally, there is an interval
migration process which can be used to free space on volumes during
times of high activity.
• Expiration proc essing
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 expirationof a data set is determined by
the Management Class attributes for that data set.
• Release of unused space
HSM can release over-allocatedspace of a data set forbot h 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 aref iltered;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 recoveryscenarios. HSM can then restore the volumes and recover the data
sets when they are needed.
• Incremental backups
This is the process of takinga copy of a data set, depending upon whetherit
has changed (open foroutput; 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. Fornon-S MS
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 existwhich des cribe how oftent he processis
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
businessc ritical,to enable recovery should a scenario arise.
4Veryl arge data sets, in excess of 64,000 track s,c annot be migrated to disk: they must be m igrated to migration level 2 tape.