Space Requirements for Indexes

Space is allocated to tables and indexes in increments of one extent, or eight pages, at a time. Each time an extent is filled, another extent is allocated. Use sp_spaceused to display the amount of space allocated to and used by an index.

In some cases, using the sorted_data option allows the SAP ASE server to skip copying the data rows. In these cases, you need only enough additional space for the index structure itself. Depending on key size, this is usually about 20 percent of the size of the table.