Organizing disks into a redundant array decreases the total usable storage capacity. For instance, a 2-disk RAID 1 array loses half of the total capacity that would have otherwise been available using both disks independently, and a RAID 5 array with several disks loses the capacity of one whole disk. Other types of RAID arrays are arranged so that they are faster to write to and read from than a single disk.

There are various combinations of these configurations giving different trade-offs and benefits of protection against data loss, capacity, and speed. RAID levels 0, 1, and 5 are the most commonly found, and cover most of the typical requirements.

• RAID 0 (striped disks) distributes data across several disks in a way that gives improved speed at any given instant. If one disk fails, however, all of the data on the array will be lost, as there is neither parity nor mirroring.
• RAID 1 mirrors the contents of the disks, making a 1:1 (1 to 1) ratio real-time backup. The contents of each disk in the array are identical to that of every other disk in the array.
• RAID 3 uses a striped set with dedicated parity or bit interleaved parity or byte level parity.  This mechanism provides fault tolerance similar to RAID 5. However, because the strip across the disks is a lot smaller than a file system block, reads and writes to the array perform like a single drive with a high linear write performance. If one drive fails, the performance doesn't change.
• RAID 5 (striped disks with parity) combines three or more disks in a way that protects against data loss of any one disk. The storage capacity of the array is reduced by the capacity of the one disk (all disks are of equal size).
• RAID 6 (striped disks with dual parity) can recover from the loss of two disks.
• RAID 10 (or 1+0) uses both striping and mirroring. ("01" or "0+1" is sometimes distinguished from "10" or "1+0": a striped set of mirrored subsets and a mirrored set of striped subsets are both valid, but distinct, configurations.)