A couple of weeks ago suddenly D: vanishes. Shut down, can see it OK in POST, but not in windows. Using Hitachi utility could see no drives attached to system. Couple of reboots later everything back to normal, so put it down to one of those things.
Last night does it again, except this time not visible in POST. Swapped data cables between drives and both visible. Swapped them back and everything booted OK.
This evening I couldnt see the drive on the network and found the sharing settings had gone.
I'm thinking drive is on its way, but wouldn't mind everyones thoughts.