A set of multiple disks that exchange data in such a way as to permit the failure of at least one without losing any data. There are multiple levels of RAID, including:
0- Striping, where data is simply striped across multiple disks to make one larger logical file system; no parity information is used; one dead disk takes out the whole array
1- Mirroring, where one disk is duplicated onto another disk; if either disk fails, the other disk has all the data (no data is lost)
2- Parity (proprietary), special case. Patented by Thinking Machines, Inc. Hamming code disk array which consists of data drives and multiple parity drives.
3- Striping with parity, where one disk in an n-way stripe is reserved for parity information (also known as byte striping)
4- Striping with parity, where one disk in an n-way stripe is reserved for parity information, using a variable striping unit size (also known as segment striping).
5- Striping with parity, where information (including both data and parity) is striped across all disks in an n-way stripe
S- Striping with parity (proprietary), where information (including both data and parity) is striped across all disks in an n-way stripe; proprietary to EMC Corp. (no longer in use)
6- Segment striping with multiple parity, an improvement on RAID 5 by having multiple parity drives, allowing for multiple disk failures with no data loss
7- Striping with parity (proprietary), a method patented by Storage Computer Corp. where data is striped across multiple drives with one or more parity drives (an unofficial RAID level)