Allocating and extending data sets

Primary and secondary allocation sizes are the main factors that affect the amount of disk space that Db2 uses.

In general, the primary allocation must be large enough to handle the storage needs that you anticipate. The secondary allocation must be large enough for your applications to continue operating until the data set is reorganized.

If the secondary allocation space is too small, the data set might have to be extended more times to satisfy those activities that need a large space.

IFCID 0258 allows you to monitor data set extension activities by providing information, such as the primary allocation quantity, maximum data set size, high allocated space before and after extension activity, number of extents before and after the extend, maximum volumes of a VSAM data set, and number of volumes before and after the extend. Access IFCID 0258 in Statistics Class 3 (SC03) through an IFI READA request.