So I have minimal experience setting up hard drive raids. I have done Raid 0 and Raid 1 configurations. I have been researching various other configurations, but am not 100% clear if what I want to do is possible or not. I think what I want is Raid 4, but I just thought I would pick some more experienced brains before purchasing the drives.
I built a system with the HAF-XM, which has two hot swap bays built into the front of it. What I want to do is setup an internal hard drive raid 0 with 2 x 2tb drives inside the case and one 4tb drive in the hot swap bay. I want the 4tb to be a raid 1 mirror of all the data on the the raid 0. Is this possible with Raid 4 or am I barking up the wrong tree? I am running OS X.
OSX doesn't do RAID4 (OSX only does RAID 0 and 1), and what you want isn't RAID4 anyways. Are you using an internal RAID controller of any kind? If not, then your options are limited to RAID0 and 1. Also, for the most part, it is not only best practice but also mostly required to use the same capacity drives for all members of your RAID, because it almost always will limit that 4TB drive to 2TB of use because 2TB is the smallest member. Your other options are (not as good) get a RAID software of some kind and do a RAID5 with 3 2TB or 3TB drives. That will give you 4TB or 6TB usable, respectively. Or, another (better) idea is to get an internal RAID controller and do a RAID 5 with the 3 drives that way. I recommend RAID controller card. More stable.
RAID5 allows you to lose one disk and still be able to access your data, which is why even though you have 3x 2TB drive, you only have 4TB usable. It uses that third drive for parity. This is the same capacity you seem to desire, anyways. http://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_5