RAID
RAID stands for Redundant Array of Inexpensive Drives. Different RAID setups allow varying levels of redundancy when setting up drives for data storage. The most common setups for standard consumer use are RAID 0 and RAID 1.
RAID 0
No actual drive redundancy, just split data between two drives by copying alternating bytes to each disk (more or less). This increases performance since both drives can be working to read/write the same amount of data, but if one of the drives fail all data is still lost (since each half of the data on the drives is useless on its own). Alternating the storage of bytes in this way is generally referred to as stripping.
RAID 1
Pretty standard redundant setup, but slower and more costly than RAID 0. With two disks, all data that is copied to the first disk is also copied to the second disk. While this will slow down write times, I believe in theory read times could be just as fast as RAID 0 (if software supposed reading alternating chunks from each drive instead of just a single drive). This performance descrease comes with increased redundancy; if either drive fails, you now have a perfect copy on the other drive ready to go.
Nested RAID Levels
Interestingly, you can nest different RAID levels (usually requiring a larger number of disks) to increase performance while still acheiving redundancy. For example, RAID 0+1 makes a redundant (RAID 1) copy of a RAID 0 setup (using four drives in total). This way, you can get the performance benefits of RAID 0 while ensuring you don’t lose all of your data should one drive fail. A RAID 1+0 setup acts in the same way, swapping the role of the RAID setups.