Hello everyone,
I apologize if this has already been mentioned but this problem has annoyed me for the last 36 hours and now I have finally found a solution. So in the hope of saving countless of hours for countless of people (when I come to think of it, I am actually saving lives here;) here is my problem and the simple but not obvious (to me) solution.
The problem: I bought a DNS-325 and 2 3TB WD Caviar Green drives (running latest official firmware) and when I powered on the DNS-325 only the left disk shows up. The right disk cannot be seen, and the right LED is not on. I tried changing the disks, but the same result.
The solution: Go ahead and format the only disk (the left one) showing up. Once you are finished formatting the disk as a standard volume, power off the NAS, and switch the disks. Once you power on the NAS, you will now see both disks, and you can go ahead and format both of them, and select the RAID level you want.
I hope it helps someone. =)
Best regards,
Dan