StorageManagementwith DFSMS 45
Electing DB2 toselect the volume requires assigning a Storage Class with
guaranteed space.However, guaranteed space reduces the benefits ofSM S
allocation, so thisapproach is not recommended.
If you do choose to use specific volume assignments, additionalmanual space
management must be performed. Unlike non-SMS, SMS does not retry to skip a
volumethat cannot satisfy the requested space. Free space must be managed for
each individualvolume to prevent failures during the initial allocation and
extension.This will generallyrequire more time for space management, and will
result in more space shortages. Guaranteed space should only be used where
the space needs are relatively small and do not change.
Toidentify and reference a particular Storage Group, a uniqueone to eight
character name is used, for example, SGDBFAST.
Table11 provides a list of attributes for consideration.
Table11. Storage Group Attributes
For further information on all SMS Class attributes and definitions,s ee
DFSMS/MVS DFSMSdfp Storage AdministrationReference, SC26-4920.
5.3.4.3 Mapping Devices to Storage Groups for Performan ce
From theperformance point of view, migrating to SMS offersthe opportunity to
automatically set DB2 allocations to predefineddisk areas. Each storage server
offersa predeterm inedlevel of parallel access. For example, the RVATurbo
allows eight concurrent datatransfers to and from the host. DB2 administrators
and storage administratorsc an distributethe Storage Groups to maximize the
use of parallel capability offeredby each storage server type. For example, with
RVAservers, a Storage Group should have a multipleof eight volumes per RVA
and be spread over severalRVAs. A performance oriented small Storage Group
could havejust eight volumes defined per RVA (ingroups of two by LCU, and by
RVA)and spread over the number of RVAs required forbest parallel access.
SMS offersa performance oriented automated allocation mechanism provided
that a defined Storage Group logical topologymatches the c urrentinstalled
ATTRIBUTE COMMENT
AutoMigrate Specifieswhether migration should be permitted on
thisStorage Group.
AutoBackup Specifieswhether backup should be performed on
thisStorage Group.
AutoDump Specifieswhether full volume dumping should be
performedon this Storage Group.
MigrationThreshold
(High and low)
Apercentage figure which when exceeded forces
migrationto occur. Likewise,a percentage figure, at
which migration stops.
DumpClasses Specifiesthe frequency of auto dumping, if required.
GuaranteedBackup Frequency Specifiesthe maximum number of days that can
elapsebetween backups. NOLIMIT indicates data
setsin the Storage Group are backed up according
totheir Management Class.