RAID

Well talking about performance i could not skip out of understading what RAID means and how it works i always knew it expanded as Redundant Array of Inexpensive Drives. It is a technology which allows simultaneous use of one or more disk to achieve higher performance, reliability or volume size.

When several physical disks are set up to use RAID technology, they are said to be in a RAID array. This array distributes data across several disks, but the array is seen by the computer user and operating system as one single disk. Several arrangements are possible and these arrangements are called RAID configurations we assume here that all the disks involved are of the same capacity. The most popular of the RAID configurations are 0,1 and 5:
1. RAID 0 (striped disks) distributes data across several disks in a way which gives improved speed and full capacity, but all data on all disks will be lost if any one disk fails.


2. RAID 1 (mirrored disks) uses two (possibly more) disks which each store the same data, so that data is not lost so long as one disk survives. Total capacity of the array is just the capacity of a single disk. The failure of one drive, in the event of a hardware or software malfunction, does not increase the chance of a failure or decrease the reliability of the remaining drives (second, third, etc).





3. RAID 5 (striped disks with parity) combines three or more disks in a way that protects data against loss of any one disk; the storage capacity of the array is reduced by one disk. The less common RAID 6 can recover from the loss of two disks.



RAID IMPLEMENTATIONS
RAID combines two or more physical hard disks into a single logical unit by using either special hardware or software. Hardware solutions often are designed to present themselves to the attached system as a single hard drive, and the operating system is unaware of the technical workings. Software solutions are typically implemented in the operating system, and again would present the RAID drive as a single drive to applications.

RAID involves significant computation when reading and writing information. With true RAID hardware the controller does all of this computation work. In other cases the operating system or simpler and less expensive controllers require the host computer's processor to do the computing, which reduces the computer's performance on processor-intensive tasks