5220 PureDisk Volume Down

Hi,

I have 2x5220 Master / Media appliances running 2.5.1 with external storage units, the PureDisk Volume is going down on one or other of the appliances every few weeks, it usually takes multiple reboots / full shudown to get it back up but it's hit and miss, I have no definitive process for bringing it back online. How do I troubleshoot ? what logs should  I be looking at ? is there a correct way of bringing a PureDisk Volume back up ?

Thanks,

Dec