Regarding this question about WD drives...
Folks, this is a problem with WD. Specifically, sometime in early 2009 they made a decision to intentionally cripple the firmware in their non-enterprise (i.e., Caviar) product line in a way to make them ONLY function reliably as stand-alone drives in desktop applications. No RAID functionality.
The reason for this was to protect the market space for the more expensive enterprise class RE3/RE4, etc. drives. Think about it -- why would somebody want to pay 20-30% more for enterprise-class drives for a clustered storage/RAID application when the cheaper desktop drives function just as well? Solution -- make the cheaper desktop drives NOT FUNCTION SO WELL in those type applications (RAID).
One of the ways WD did this was by disabling a feature known as TLER (Time Limited Error Recovery) on the Caviar drives. Google it for details. Causes drives to drop out of RAID arrays when they encounter read error lasting more than a few seconds (actually, 7 seconds). Thus forcing you to unplug the drive from the hot-swap backplane, plug it back in and force a rebuild, whereafter it functions just fine for a while (sometimes weeks) then does it again.
How do I know all this? Because I just built a new Windows 7 (64) PC using an ASUS mb with an Intel RAID controller and a Corsair chassis with a SATA II hot swap backplane and made the mistake of selecting 4 WD 1TB Caviar drives for my 2TB RAID 10 array. Everything works great for 2, sometime 3 weeks then I will lose a drive from the array, have to hot re-plug and re-build it in Intel RST v9.6. I did a lot of research on it and discovered the TLER issue. Used WD tools to probe the time limedted error recovery parameter in the firmware on my drives. It was turned off and DISABLED in firmware.
One of the things that sort of obfuscates the issue and masks WD's involvement in this is that prior to about August 2009, the TLER parm was totally functional and yes, you could buy a cheaper Caviar drive, stick it in a RAID array and everything would be great. Those were the days. Then WD started turning TLER off in firmware and a few months later, actually DISABLED (crippled) the TLER parm in the firmware so you couldn't turn it back on, even with the correct WD utilities (which about the same time, disappeared from WD's download site).
So, if you have a Caviar drive made before a certain date, you may have no problems at all running it in a RAID configuration. But you WILL have a problem if you use recent, current production WD non-enterprise drives.
WD changed their marketing or sales materials to start using the work "desktop" a lot more in the product description of the Caviar drives. At the same time, they are now trumpeting the RE3/RE4 enterprise class drives as being "TLER enabled". Whatever...
Myself, I am ditching my TLER disabled but otherwise fully functional 1TB WD Caviar Blacks when I get the chance for a pair of Seagate Barracuda or Hitachi"s. And that *especially* applies to the drive selection for my soon to be acquired the DLINK DNS-323 NAS as well. Just wish I had known all this 4 months ago before I made a $450.00 mistake purchasing WD Caviar drives for RAID 10