ExtremeTech uploaded a RAID 101 guide, you can read it over here.
Anyone who's ever looked into purchasing a NAS device or server, or even played around with installing internal hard drives, has undoubtedly stumbled across the term "RAID." RAID stands for Redundant Array of Inexpensive Disks," and generally uses two or more hard drives to improve the performance or provide some level of fault tolerance for a machine.
It's a good thing to be aware of the various RAID options out there, but because there are so many, learning all the ropes can be a bit confusing. What follows is our attempt to break it down for beginners, to help make it clearer what RAID is and why you may need (or want) it to keep your data secure and speedy to access.