I'm using a hardware HP RAID controller. My server came with one 250GB drive. I purchased three additional 250GB drives with the intent of having one as a cold-spare.
I put the two additional drives in the server and powered it up. I went into the BIOS, enabled the RAID controller, then rebooted. It brought me to the HP raid controller setup. I went in and deleted the three pre-existing arrays (which were just three drives operating independently of each other). I then selected the array configuration option, selected all three drives together, and told it to initialize. It did its thing, then I went into "create array" and again selected all three drives. It presents me with a dialog asking what kind of RAID that I want to set up, but the problem is that it doesn't present RAID 5 as an option. All I can choose is 0, 1, and 10.
I know RAID 5 is possible with 3 drives, so what gives? I've never set up a RAID array before so if there is something obvious I'm missing here don't hesitate to tell me...
Your RAID controller doesn't support RAID 5.
As others have said and you have witnessed by "All I can choose is 0, 1, and 10." You'll need a different controller that supports RAID 5. You'll need to get with your VAR or HP and find one compatible with your server model.
It's possible that your RAID controller does not support RAID 5. Sometimes they will be a 'light' model that only supports 0/1/10 until it's upgraded either with a license or hardware key.