Drobo gen 2 sudden slow speed

Suddenly the drobo gen 2 speed dropped to 8-10 MBps but none of the light is red or blinking. Any ideas how I can identify the disk with problems?

Can you advise what OS you are running? Is this connected via firewire or USB 2.0? USB 2.0 maxes out around 18-20 MB/s. Have you filed a case with support to review this further?

Tried all connections. Same. How do I identify the bad disk? Support is not helping because it is out of warranty.