11 disks in a RAID6? I have always seen even numbers. ie 6+2 8+2 etc. Not saying that is the issue. Remember that RAID6 is slower than RAID5. RAID5 calculates the parity once. RAID6 does it twice. This is to make sure that you have parity protection incase you drop a drive. I would only recommend RAID6 on large drives (1TB or larger).