The Raid 1 setup in my server has been driving me nuts.
It failed to build so I figured it was time to replace the two Samsung 250Gb drives wth two Western Digital 500Gb Caviars Raid Edition 2's. I needed the extra space anyway.
I bought the drives from scan.co.uk along with a new 150Gb Raptor. After a pile of testing, they all proved to be duds and I RMA's them back. Couldn't believe I could get three bad hard disks in a row.
I got two more Western Digitals Caviars and went through more testing - mostly using the Western Digital Data Lifeguard Diagnostic for Windows. It's turns out that if there is one bad sector in either disk you're using to build a mirror, the build will fail. Read KB325615.
A bad sector can get remapped at both a file system level and by the hard disk firmware. For a RAID 1 build, it's got to be done at the firmware level. This requres the disk to first read and then write to that bad sector. I found that if I ran the diagnostic tool to do an extended test followed by a write zero's test, I could eventually get rid of a few bad sectors.
For one drive it took about 37 hours for each test. What a pain! It took about two weeks of messing about to finally get the RAID 1 drives rebuilt and loaded up.
UPDATE
I've given up on RAID 1. Now I'm just doing a weekly (or so) backup of the drive using "robocopy /mir". It's a fast and simple solution.