For nonstriped VSAM data sets, space is allocated to system-managed multivolume data sets with the guaranteed space attribute in the storage class, as follows:

• Initially, primary space is preallocated on all the volumes.
• When the primary amount on the first volume is used up, a secondary amount is allocated on the first volume until the volume is out of space or the data set has reached its extent limit.
• The preallocated primary space on the next volume is then used.
• When the primary space on the next volume is used up, a secondary amount is allocated.
• Secondary amounts continue to be allocated until the volume is out of space or the data set extent limit is reached. For a non-EA data set, if the extend fails, the system attemps to extend to a new volume by the primary amount.