Archive for the ‘RAID basics’ Category

What is RAID:

RAID stands for Redundant Array of Independant Disks previously known to be Redundant Array of Inexpensive Disks. First to explain RAID – what is it and what is it used for, let me clear you what does physical and logical drives in a computer system means.

A physical drive signifies the hard disk inside the computer cabinet. The physical part of the computer. It may be one or two in number.i.e., the physical drive is the real one as you see it inside the computer as a part of it.

In contrast, a logical drive is that which is a virtual representation of your physical drive. It is the drive(s), as seen by the operating system of your computer system.

An example might clear the cloudy thoughts about the physical and logical stuff concerning drives. Consider an  example, of a laptop, it has only one hard disk inside it, but when you partition it, such as C:, D: etc., now, the original drive inside the laptop is the physical disk and the C:, D: are called logical disks. I mean if you have four partitions, and one hard disk, you have one physical disk, which is divided into four logical disk… Now i think it will be clear that the logical disk is nothing but the physical disk as seen by the operating system.

Comming to RAID, it is the technology used to deploy the hard disks for increased storage and or or redundancy. Here R signifies redundant which means backup or duplicating. Here in RAID, we use two or more physical drives, and use RAID configuration to make the operating system believe that there is only one hard disk.(i.e., logical drive) many configurations are available in RAID such as RAID 0, RAID 1, RAID 2, RAID 3, RAID 5 etc… let me introduce RAID 0 and RAID 1 which will suffice the basic knowledge to RAID.. if you want more info on RAID, head to wikipedia and google is also there to help you.


In this configuration, two hard disks are used. Here, data is split and written on both harddisks simultaneously. i.e., for example, take a file, if it is split up into 4 parts A,B,C and D, A and C go on one hard disk and B and D go in other hard disk. As data is written paralley, great speed is achieved. If it is to be stored on a normal hard disk(written in serial fashion), the data takes 4 seconds to record( assuming that each part takes one second to be written[though its fairly a too large time]). But in RAID 0 configuration of two disks, it takes only 2 seconds.. wow, how fast!. The advantages are fast and inexpensive. But the disadvantages are its not reliable.. because, if one hard disk fails, then total data is useless and lost. RAID 0 is illustrated below.


Here, same as RAID 0, two hard disks are used. But instead of splitting and recording the data, the same data is written twice in the two hard disks i.e., one hard disk is exact duplicate of the original one. This provides redundancy, i.e., when one hard disk fails, no data is lost and thus data saftey is provided. The advantages here is mainly redundancy.. it is safe i.e, you wont loose your data till atleat one of the hard disk is alive and runnig up fine. The main disadvantage is the very slow writing speed coz, the data is written two times,and also cost of the drive matters. The below pic gives a clear view of RAID 1 config