I have trouble with the original disks within my Buffalo Linkstation Duo. The two 500GB original hard drives that came with my drive failed one after another (luckily, not together!). Be fair to Buffalo, their after sale service is good (well for the first replacement). Emails were replied promptly - though I have problems with the second replacement, their customer services team is good, but their RMA team is dreadful. I had waited for over two months for a reply from them.
Anyway, the reason I wrote this post is that I was fed up the waiting for the replacement and decided to use two spared 250GB drives I have to safe keep my files. I need the fail-safe provided by RAID1.
Unfortunately, it is not easy as putting two empty drives into the unit and configure the NAS. It seems Buffalo stores the OS of the NAS on the hard drive rather than on the drive's ROM. Hence, if you have replaced both drives, the NAS will not know what to do at the boot time.
If you really need to replace both drives at the same time, you need to use TFTP to transfer essential files to the NAS to make it operative. Step can be found at: http://forums.buffalotech.com/t5/Storage/FAQ-3-of-5-TFTP-boot-procedure-please-read-this/td-p/68094 . There is a point you made want to note. You don't need to take the drive off your network. In fact, it is better to keep it in your network as after receiving the necessary files through TFTP for booting, it will try to obtain an IP from your DHCP server. If the drive is still in your network, it can get an IP from your DHCP server. All you need to do is to set you PC to the static IP 192.168.11.1 to allow the NAS to locate the files intially.
If everything went well, you should have your Buffalo drive in EM mode, and your PC is at static IP 192.168.11.1 . Now, you can put your PC back to your network, i.e. use your normal IP (from DHCP or a static IP within your subnet).
The next step is to run the firmware updater in debug mode, and the instructions can be found at this video:
With the debug mode, you can ask the NAS to rebuild the drives partition and put back all necessary files onto the hard drive for normal boot.