User Guide

SAP AG November 2002
and informs the transaction of the log sequence number that was assigned when the log
page was written to the log area.
Volume
A volume is a logical grouping of physical storage units (disks). A volume can be a part of a
physical disk, a complete physical disk, or a completely structured storage system consisting
of several storage units.
The disks used should have identical performance parameters (specifically access speeds) to
ensure an even filling of the volumes.
If database management tools are used, a volume is addressed via a directory path.
The database system differentiates between data volumes [Page
130] and log volumes [Page
144].
Every database instance [Page
132] has one or more log volumes and data volumes. You
configure the maximum numbers of data and log volumes that are possible when installing
the database instance.
If necessary, you can add data or log volumes to a database instance while the database is
running. Directory paths for data and log volumes can be changed.
Data Volume
A database instance [Page 132] has volumes [Page 153], in which the data writer [Page 15]
records the database contents. These volumes are called data volumes. All data volumes
form the data area [Page 131].
Among other things, the data volumes contain the application data [Page 125] and the
metadata of the database catalog [Page
131].
Managing Application Data
The application data of a table or index can use just one page [Page 146] in the data area as
a minimum. A table can extend across all data volumes of the data area as a maximum. A
table increases or decreases in size automatically without administrative intervention. As a
rule, a database-internal striping algorithm distributes the data belonging to a table evenly
across all the data volumes.
It is therefore not possible or necessary to assign tables to the individual data volumes.
See: Data Management Using B* Trees [Page
101]
Managing Data Volumes
You can configure one or more data volumes when you install a new database instance. The
disk storage space defined by all the data volumes is the total size of the database.
During database operation, you can add new data volumes. The number of data volumes is
limited by the database parameter MAXDATAVOLUMES [Page
85].
See:
Database Manager GUI: SAP DB 7.4, Section Managing Database Instances [See SAP DB
Library]
Database Manager CLI: SAP DB 7.4, Section Adding a Volume [See SAP DB Library]
User Manual: SAP DB 21