DB2Storage Objects 13
DB2 V6 has increased the maximum size of a partitioned table space to almost
16 TB, increasing the maximum data set size to 64 GB. This is supported only if
they are defined and managed with DFSMS 1.5.

3.2.3 INDEX

A table can havezero or more indexes. An index contains keys. Each key may
point to one ormore data rows. The purpose of indexes is to establisha way to
get a directand faster access to the data in a table. An indexwith the UNIQUE
attribute enforcesdistinct keys and uniqueness of all rows in the referenced
table.An indexwith t he CLUSTER attributecan be used to establish and
maintain a physicalsequence in the data.

3.2.4 INDEXSPACE

An index spaceis used to store an index.An index space is physically
represented byone or more VSAM LDS data sets.
When a non-partitioning index needs to be split across multiple data sets in order
toi mproveI/O performance, these particular type of data sets are called PIECEs.
DB2 V5 has introducedthe capability of defining up to 128 pieces with a
maximum size of 2 GB. DB2 V6 and DFSMS 1.5 increase the limit to 254 pieces
of up to 64 GB.

3.2.5 DATABASE

A database is a DB2 representationof a group of related objects. Each of the
previouslynamed objects has to belong to a database.DB2 databases are used
to organizeand manage these objects. Normally a database is the association of
table spaces and indexspaces used by an application or a coherent part of an
application.

3.2.6 STOGROUP

A DB2 StorageG roup(STOGROUP) is a list of storage volumes. STOGROUPs
are assigned to databases,t ablespaces or index spaces when using DB2
managed objects. DB2 uses STOGROUPsfor disk allocation of the table and
index spaces.
Installations that are SMS managed can define STOGROUP with VOLUMES(*).
This specification impliesthat SMS assigns a volume to the table and index
spaces in that STOGROUP.In order to do this, SMS uses ACS routines to assign
a Storage Class,a Management Class and a Storage Group to the table or index
space.
3.3 Creating Table Spaces and Index Spaces
Tableand index spaces can be created in one oft woways:
• DB2 defined and managed
• User defined and managed
See the DB2 for OS/390 Administration Guide, SC26-8957,Chapter 2, Section
2-7, "Designing StorageGroups and Managing DB2 Data Sets",for a detailed
explanationon t his subject.