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Software-RAID HOWTO

Linas Vepstas, `[email protected]`

v0.54, 21 November 1998

RAID stands for ''Redundant Array of Inexpensive Disks'', and is meant to be a way of creating a fast and reliable disk-drive subsystem out of individual disks. RAID can guard against disk failure, and can also improve performance over that of a single disk drive. This document is a tutorial/HOWTO/FAQ for users of the Linux MD kernel extension, the associated tools, and their use. The MD extension implements RAID-0 (striping), RAID-1 (mirroring), RAID-4 and RAID-5 in software. That is, with MD, no special hardware or disk controllers are required to get many of the benefits of RAID.

Preamble

This document is copyrighted and GPL'ed by Linas Vepstas ( [email protected]). Permission to use, copy, distribute this document for any purpose is hereby granted, provided that the author's / editor's name and this notice appear in all copies and/or supporting documents; and that an unmodified version of this document is made freely available. This document is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY, either expressed or implied. While every effort has been taken to ensure the accuracy of the information documented herein, the author / editor / maintainer assumes NO RESPONSIBILITY for any errors, or for any damages, direct or consequential, as a result of the use of the information documented herein.

RAID, although designed to improve system reliability by adding redundancy, can also lead to a false sense of security and confidence when used improperly. This false confidence can lead to even greater disasters. In particular, note that RAID is designed to protect against *disk* failures, and not against *power* failures or *operator* mistakes. Power failures, buggy development kernels, or operator/admin errors can lead to damaged data that it is not recoverable! RAID is *not* a substitute for proper backup of your system. Know what you are doing, test, be knowledgeable and aware!