while I was trying to extend a RAID1+0 on a P400 in a DL380 G5
I shortly realized something is missing in the ACU.
The Extend Array Button was missing, after reading in detail
the manual to ACU I found this HP P400 Overview.
That finally means no Extend Array Button when the BBWC(Battery Backed Write Cache) option is faulty or missing.
bob the building master 