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MegaRAID Storage Manager Online Help System |
Understanding RAID Levels
RAID means Redundant Array of Independent Disks. When you create storage configurations you can use several different types of RAID technology, called RAID levels, to create multiple-disk arrays on which data will be stored. The computer operating system sees each array as a single virtual disk, not as a collection of individual disk drives.
- A RAID 0 array has two or more disk drives. Data is divided into small blocks (stripes) that are written successively to all the disks in the array. Thus, at the same time data block #1 is written to disk1, data block #2 is being written to disk2, and so on. This is obviously faster than writing an entire file to one disk drive, and reading files is faster as well. RAID 0 is a good choice if fast read/write capability is the most important objective. However, RAID 0 arrays are not fault tolerant and cannot be protected with hot spare disks.
- A RAID 1 array has exactly two disk drives. Data is written simultaneously to both disks, so that one disk is a mirror of the other. If one of the disks fails, the data is still protected. A hotspare disk can be used to automatically replace a failed mirrored disk. RAID 1 provides a high level of data protection. However, data writes are slower than with a RAID 0 array because all data must always be written to two disks. Also, the two-disk RAID 0 array has only one disk of actual capacity.
- A RAID 1E array is the same as a RAID 0 array, except that the data is divided into stripes, and each stripe is then written to one disk and mirrored on another disk. Thus, the data is protected by the mirroring arrangement. As with RAID 1, if a disk in the array fails a hot spare disk can automatically replace it. RAID 1E performance is roughly the same as for a single drive, although in some instances the dual write may be somewhat slower.
DB09-000202-00 July 2007 Copyright© 2007 by LSI Corporation. All rights reserved. You can find a list of the LSI U.S. distributors, international distributors, sales offices, and design resource centers on the LSI web site at: http://www.lsi.com/cm/ContactSearch.do |