Specify which, if any, disk set your new component should belong to. Only disks and slices belonging to the specified disk set will be available, if you choose to use a disk set.
A disk set, is a set of shared disk drives containing logical volumes (RAID 0, RAID 1, RAID 5, transactional devices), state database replicas, hot spares, and soft partitions that can be shared exclusively, but not concurrently, by multiple identical hosts.
If you do not have multiple hosts that share access to a storage array, choose No Disk Set.
If you have an existing disk set that you want the new volume associated with, choose Use Existing Disk Set
If you need to create a new disk set with which this volume should be associated, choose Create New Disk Set