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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 00 array is a spanned array that creates a striped set from a series of RAID 0 arrays.
- 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 10 array is a spanned array that creates a striped set from a series of mirrored drives. The array can sustain multiple drive losses as long as no two drives lost comprise a single pair of one mirror.
- A RAID 5 array requires a minimum of three disk drives. Blocks of data and parity information are written across all drives. The parity information is used to recover the data if one drive fails in the array. A hotspare disk can be used to automatically replace a failed disk. The disadvantage of RAID 5 is a relatively slow write cycle (2 reads and 2 writes are required for each block written). RAID 5 is best suited for networks that perform many small I/O transactions simultaneously. Since each drive contains both data and parity, many writes can take place concurrently.
- A RAID 50 is a spanned array in which data is striped across multiple RAID 5 arrays. Thus, RAID 50 provides the features of both RAID 0 and RAID 5. RAID 50 breaks up data into smaller blocks, and then stripes the blocks of data to each RAID 5 array. A minimum of six disk drives is required. RAID 50 can sustain one to four drive failures without losing data, if each failed disk is in a different RAID 5 array.
- A RAID 6 array, which requires a minimum of three disk drives, is similar to a RAID 5 array. Blocks of data and parity information are written across all drives. The parity information is used to recover the data if one or two drives fail in the array. A hotspare disk can be used to automatically replace a failed disk. RAID 6 provides more data protection than RAID 5; the data is still safe if a second disk fails while the first failed disk is being rebuilt.
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 |