Well for the moment ignoring the god awful configuration you have been sold
What HPE tried to describe to you is correct, they should maybe have been more verbose.
You have a CPG with a policy to make sure that logical disks making up your volumes span 8 physical disks.
How will follow that policy with one disk missing ?
(next bit is simplified to save fingers typing ...)
You know how when a volume is created 2 logical disks get created (one per node and each probably 16GB in size) from chunklets, then your volume basically gets striped across those volumes and starts using capacity, when the LD capacity is used up the system tries to grow them and follows the rules of the CPG to make sure the growth spans 8 physical disks .. which if a disk is failed (leaving you with only 7) it can no longer do so, it can't grow, then of course the volume itself that prompted the LD growth has but none made available to it and fails.
Verdict ... change your CPG to 6+1 and tune your volumes to the new policy if you want things to still work after a single disk failure.
Better verdict ... use smaller capacity disks but more of them.
- those big SSDs look tempting but are only any good if you have lots of them for your system to work with.
- honestly your array config is dreadful and should never have been sold to you like that it's just plain wrong (OK rant over
Mark