January 18, 2007

What is RAID?


RAID is the abbreviation for Redundant Array of Independent Disk, the technology that store data with a high degree of data protection or performance than regular storage. RAID works on a concept of Data Mirroring that means making simultaneous writes of the same block of data on multiple disks. It is expensive, but data intensive application such as account, finance, and banking, where in case of a hard disk crash, data can be restored from a mirrored disk.

There are many different levels of RAID. Typical examples are RAID 0, RAID 1, RAID 0+1, RAID 3+0 and many more. At each level RAID takes a different approach to the storage of data. As mentioned RAID works on the concept of data mirroring, data striping and parity checks, that is where the levels comes. RAID 0 uses only striping, RAID 1 uses mirroring and further levels include parity checks or combination of these, you get many permutation, but RAID always use at least two hard disks that works as a single unit.

RAID that can do-RAID levels, 0+1, 1, 1+0, 5, 6, 5+0 and 5+1 allows a single hard disk to fail while keeping the data as the system accessible to users. Users in general would not realize disk failure; and would continue to work normally. The use of RAID allows the disk in problem to be changed, and data restored and updated, without hampering the work. Data from the working disk can be mirrored back on the new disk.

In RAID levels that use striping (RAID 3) at the byte levels each byte of the stream is stored on a different disk; at the disk level (RAID 2) data is broken down in to bits, and stored on different disks. This is very useful in application with large image files as well as video editing application, which demand good amount of speed.

RAID that can not-RAID can help in the recovery and restoration of data, but it can not protect these data. It cannot stop virus or malicious code from attacking. Any such attack will cause simultaneous and equal harm to all disks. RAID cannot provide a performance boost to all running application. Increasing in the data transfer rate dose little to help desk top users, since most files that are accessed are typically very small. Raid systems are not easily interchangeable unlike the case with single disk. The RAID BIOS, which controls the read/write of the data to the disks in the array, must be made available to the operating system.

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