When you add a new device to a database, Adaptive Server places the new device in a default pool of space (the database’s default and system segments). This increases the total space available to the database, but it does not determine which objects will occupy that new space. Any table or index might grow to fill the entire pool of space, leaving critical tables with no room for expansion. It is also possible for several heavily used tables and indexes to be placed on a single physical device in the default pool of space, resulting in poor I/O performance.
When you create an object on a segment, the object can use all the database devices that are available in the segment, but no other devices. You can use segments to control the space that is available to individual objects.
The following sections describe how to use segments to control disk space usage and to improve performance. “Moving a table to another device” explains how to move a table from one device to another using segments and clustered indexes.
