Extra space on disk after RAID 5

Hello Everyone,

I am currently setting up my second, and hopefully first successful, RAID ever. Last RAID I tried was just a RAID 0 but cause of a faulty RAID controller it failed.

Anyways, this time I am doing RAID by the motherboard. I have four hard drives, 2x2TB WD Green, 1x2TB Samsung, 1x3TB WD SE.

I thought that since the drives are not equal, the last 1TB on the 3TB drive would just be lost, but that doesn't seem to be the case. My system offered to let me install Windows on it. I was wanting to make sure this is right, and that its safe to use that part of the drive. Please let me know.
 
Solution
Nevermind, question has been rendered mute. I guess I should have finished setting up drivers before asking. The availability of the remaining 1TB of space was removed once I installed the driver that enabled the RAID to be seen by Windows.