Tl;dr Why would someone preconfigure a hardware raid on a server AND NOT TELL ME?

Recently we got a refurbished server that has some nice specs and works quite well. It had six 2.5 bays and came with two 248gb HDDs. But it only included 2 rails, so we needed more, and we got more.

I installed windows on it (yes, some of the software we use is windows only), and for some odd reason the forth HDD (this was the second one that was pre shipped) wouldn't show up in the disk management, which was odd especially considering the fact that the SAS did detect it, and would get pissed at me if I took it out. I was in a rush so I left it alone for then.

I had needed to setup a raid for these, and while I was trying to figure out what was wrong, I noticed that windows can do a software raid so I set it up on the third HDD (which is the first pre included HDD). I haven't actually used it yet.

At some point I stated to mess with the HDD that wasn't showing up (switching them around, etc.), when I noticed that windows saw the raid was setup on both of the HDDs, which made me wonder what was going on.

So I decided to check the SAS to see if there was something wrong there, as it was booting, bios let me know that there was a raid that was in the process of rebuilding, so then I thought "oh cool, windows actually does a hardware raid!" Well actually it doesn't, as I was looking I saw that this raid was only setup on the two HDDs that were acting funny, and therefore it was only coming up as one device in windows. I wasted an hour trying to find that!