I have the same problem with a RAID5, four drives, two have lost the W in the RAID software but both drives are active in the system.
I have a RAID 01 (which the intel controller calls a RAID 10) with 4 drives; two adjacent drives have the same problem:
Two drives in the array show up as normal, and two show missing - then below that, the two "missing" drives are listed as non RAID drives. The serial numbers of the drives themselves are all correct, but it is as if the controller has corrupt information regarding the serial numbers of the two drives it thinks are missing. The controller is looking for drives that have no leading "W" and have a colon (":") preceding the last character of the serial number.
I so hope this is fixable as I transferred my entire electronic existence onto volumes on this array.
I am experience the same problem as GarageNet with my raid 0. After updating my mobo, one of the serial numbers for of the drivers in the array apears out of format when compared to the other serials.
wd-wmay011********** - the one WD in the raid
d-wmay011**********:0 - the "missing" WD from the raid
wd-wmay011********** - the "free" WD that matches ALL numbers to the missing WD, but the format of the serial is different. The "W" from the front of the serial is missing, and a ":0" at the end neither of the other WD serials have.
Also, none of these replies are "answers" as the bar at the top of the op suggests... "1 "correct" answer available (4 pts)"