EMC's implementation of   Raid  6 only  supports 4 to 16 drives that being  2+2 , 4+2, 6+2 etc.. the restriction on a 7+2 is due to how Raid 6 works see [URL]
We recently purchased and installed nine 1 TB SATAII disks (enclosure 4) in one of our CX3-20 systems. It's running FLARE 03.26.020.5.016. We were thinking we would set this up as RAID 6 7+2. When we examined our options for creating a RAID group with the navisphere manager GUI we found the choices for number of disks as follows:  8 disks : supports RAID Types : RAID 5, RAID 6, RAID 0, RAID 1/0 9 disks : supports RAID Types : RAID 5, RAID 0, RAID 3  Just want to make sure we understand why RAID 6 is not an option with 9 disks. Can someone explain?  Thank you.
CX3-20 RAID 6 question