Growing a RAID6 array on 11.10

[Steven Davies-Morris]

I have two RAID arrays on a system.  The first is RAID1 and supports 
/boot, swap / and /home.  The second is RAID6 and supports everything 
else.  It currently has 4 3TB drives.  I have 3 more sitting in the 
tower and want to add them to the RAID6 array.

I was using Disk Utility to try to add these three drives but it doesn't 
seem to want to do it with the array up and running. When I take the 
array down I'm denied access to the array controls in "Edit Components" 
so I can't tell it to add drives.

I remove the partitions from the 3 drives (initialized as GPT). Then I 
go into "Edit Components".  I see the three drives. I am told they each 
have no partitions and each have 3TB available for use.

I go to add one drive.  I click the box to add it and the click 
"Expand". I authenticate then get this message:

Error expanding RAID Array.
An error occurred while performing on operation on "hitchcock RAID6" 
(6.0 TB RAID-6 Array): The operation failed

Detail information says:

Error expanding array: helper script exited with exit code 1:
mdadm: added /dev/sdc1
mdadm: Need to backup 6144K of critical section..

I now see the new drive in the RAID6 array as a spare.

What am I missing here?  If I can't figure this out I guess it will be a 
reboot into a run-level 1 root shell to douse mdadm.  Any pointers from 
those of you who are quite familiar with using Disk Utility and RAID arrays?
-- 
SDM a 21st century schizoid man in SoCal
Systems Theory website www.systemstheory.net
"overfulnoisecascade" CD coming soon