Monday, January 28, 2008

RAID: what lies beneath????


RAID is the abbreviation for “Redundant Array of Independent Disks.” It refers to the technology of storing data with a higher degree of protection and/or performance than regular storage. A number of standard schemes have evolved which are also known as levels. Originally RAID was designed with five different levels, they being RAID 0, RAID 1, RAID 1+0, RAID 0+1, RAID 3+0. RAID combines physical hard disks into a single logical unit by using either special hardware or software. It works on the concepts of Data Mirroring, Data Striping, and Parity Checks. Different levels use different approach like RAID 0 uses only striping, RAID 1 uses only mirroring, further levels include parity checks and/or a combination of these. The configuration affects reliability and performance in different ways. RAID systems can be designed to keep working when there is failure - disks can be hot swapped and data recovered automatically while the system keeps running. Users in general would not realize that a disk has failed, and would continue to work normally. The use of RAID allows the disk in question to be changed, and the data restored and updated, without hampering work. Although RAID can help recover and replicate the data, it cannot stop viruses or Trojan horses to enter the system, and the worst part is that these malicious codes will affect all the disks in configuration equally. Today we can see various levels of RAID ranging from RAID 0 to RAID 6. Minimum number of disk required by any of this configuration is 2, with RAID 6 requiring a minimum of 4 hard disks.
For proper functioning of the RAID array, the RAID BIOS, which controls the reads and writes of the data to the disks, must be available to the operating system. With the application of RAID increasing day by day various companies have come up with their own non-standard versions of RAID, DVRAID and RAID S being a few.
 
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