When separation by volume is requested for a data set, the order of preference for volume selection is as follows:

• Candidate volumes that are in different extent pools than volumes on the separation volume list are most preferred
• Candidate volumes that are not on the separation volume list but are in the same extent pools as the volumes on the separation volume list are the next preferred
• When separation by volume is required, SMS must allocate the data set onto the volumes that are not used by any of the data sets in the same separation group
• When separation by volume is preferred, the candidate volumes that are already occupied by other data sets in the separation group are ranked lower and are less preferred.