When a multivolume VSAM data set with no extended function extends to the next volume, the initial space allocated on that volume is a primary amount. When a multivolume VSAM data set with extended format extends to the next volume, the current value of the data class option, Additional Volume Amount, indicates whether the initial space allocated on that volume is a primary amount or a secondary amount. The default is the primary amount. After the initial space allocated on the volume is used up, space is allocated in secondary amounts. The previous comments do not pertain to VSAM data that is striped. See Organizing VSAM Data Sets about VSAM data in the striped format.