duke  RAID Levels  duke


RAID
Redundant Array of Inexpensive Disks
RAID 0
Fast, but not fault tolerant and it does no mirroring nor parity calculation. It sends data to several disks at once very quickly and is typically used in film making when speed is essential.
RAID 1
Writes the same data to two disks, providing complete redundacy, but is expensive requiring double the storage.
RAID 0+1
Stripes and mirrors the data across several drives providing high performance in speed and security.
RAID 2
Stripes data across several disks at the bit level with parity saving error correction information. The problem is when the parity information is saved, the size is quite large taking 3 disks just to store the parity in a 4 disk array.
RAID 3
Stripes data at the byte level and stores parity on one disk per array. It does not allow multiple I/O operations to ber overlapped and needs sychronized drives in order to prevent performance degradation in short records. This method is most commonly used for document imaging.
RAID 4
Similiar to RAID 3 level, but stripes the data in larger chunks using a dedicated error disk.
RAID 5
Provides a cost/performance compromise. Data and parity values are striped over a minimum of 3 disks.
RAID 6
Similiar to RAID 5 level, but provides additional striping that protects you against 2 drives failing at the same time.
RAID 7
Created and patented by Storage Computer (Nashua, NH 603-880-3005) stripes data across an independent access array file like RAID 5 level but it uses more than one dedicated parity disk.

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Date of Last Revision: 21 December 2001