Db2 space allocation
Primary and secondary space allocation sizes are the main factors that affect the amount of disk space that Db2 uses.
In general, the primary space allocation must be large enough to handle the storage needs that you anticipate. The secondary space allocation must be large enough for your applications to continue operating until the data set is reorganized.
If the secondary space allocation is too small, the data set might have to be extended more times to satisfy those activities that need a large space.
You can specify the primary and secondary space allocation you let Db2 choose them. Having Db2 choose the values, especially the secondary space quantity, increases the possibility of reaching the maximum data set size before running out of extents.
If you specify the primary and secondary space allocation, you use the PRIQTY (primary) and SECQTY (secondary) clauses of the CREATE TABLESPACE, ALTER TABLESPACE, CREATE INDEX, and ALTER INDEX statements.