One for each data set or VSAM data space on the volume that has more than three extents. There can be as many as 10 for a PDSE, HFS, extended format data set, or a VSAM data set cataloged in an integrated catalog facility catalog. PDSEs, HFS, and extended format data sets can have up to 123 extents. Each component of a VSAM data set cataloged in an integrated catalog facility catalog can have up to 123 extents per volume. All other data sets are restricted to 16 extents per volume.