"Storage Subsystem implementation of RAID-1 is basically a combination of RAID-1 and RAID-10, depending on the number of drives selected. If only two drives are selected, RAID-1 is implemented. If you select four or more drives (in multiples of two), RAID 10 is automatically configured across the volume group: two drives for user data, and two drives for the mirrored data."
See Notes in :
Installation, User's, and Maintenance Guide - IBM System Storage DS3400
1. RAID 6 uses a P+Q design implementation.
2. When RAID level 1 is implemented and the number of hard disk drives increases to more than two, RAID level 10 is automatically implemented."