1 Run a full diagnositc on the failed drives to see if there way a reason for the failure. It a drive is going bad you will want to replace it.
2 What works for me is to press F whatever to get into the RAID controller at startup, remove the redundant drive(s) from the array then add them again. The RAID controller will then start the rebuild process, which will run in the backgroud as I use Windows. (it takes a log time).
You can also do this in windows using your RAID management software. The controller treats the newly added drives as blank replacements.
3 If I am 100% positive the drives were not changed in any way I delete all the drives in the array and recreate it exactly as before, but without initializing. This will instantly recreate the array without rebuilding.
Not sure what happens if you add files to an array and then recreate in this fashion. I image that every part of the array where the two drives differ will have some soft of problem.
Its been 8 months since I had to do this, but it used to happen to me all the time (I upgraded to WD RAID Edition drives.
The first thing you should do when using a new RAID controller is learn how to recreate, rebuild .. without losing data. That way when the drives are full of important data you won't make a mistake.
Obviously it would be a good idea to backup any crucial files before attempting to fix the array and to read your controllers manual.