When you see the disks showing as degraded, it means that the cache battery of the raid IOA card has failed. Normally you get a warning messge phone home to IBM telling them that the cache battery is about to fail usually 90 days before it actually fails, leaving the disk associated with that RAID card degraded. You should also get another message when it actually failed. These messages are found in the WRKPRB problem logs.
I would call your CE in right away to change the cache battery which on a 270 will require an outage to the system.