What is a Redundant Array of Independent Drives - RAID?

A redundant array of independent drives is a strategy of copying and saving data on both a primary hard drive and one or more secondary drives. Also known as a redundant array of independent disks, or RAID, this type of data arrangement provides a couple of benefits. The employment of a redundant array ensures that important data is still accessible even in the event of a failure of the primary hard drive. In addition, the overall performance of the system in regard to performing basic input/output operations is enhanced.

The arrangement of data with a redundant array is accomplished with a process known as disk striping. In layman’s terms, the storage space on each drive is sectioned or partitioned into a collection of sectors with the same storage capacity. When new data is entered and saved, the data saves to the defined sectors on each drive involved with the storage strategy. This means that when data is saved on the primary hard drive, it is simultaneously saved on each of the secondary drives.

Utilizing a redundant array to automatically create copies of important data is much easier than taking the time to manually copy data from a hard drive to a CDR or tape backup. There is no need to schedule periodic backups or to create a recurring backup that must be checked for efficiency from time to time. All of the nine different types or designs for RAID automatically alert the user if there is a failure anywhere in the process.

To the operating system driving the operation, the redundant array appears as a single hard disk drive. Each of the individual drives is accessed and read in a specified order. Since the data stripes are usually kept somewhat small, there is no loss of speed in retrieving saved data or adding additional data. When several users must have access to the data simultaneously, the stripes must be large enough to hold a complete record. Depending on the number of users logged into the system and the overall capacity of the system, retrieval and entry of data may even be quicker than with a single hard drive operation.

Along with this basic redundant array strategy, there are variations on the process that also offer some type of redundancy. RAID-1 does not employ disk striping, but does store saved data on a primary hard drive and at least one additional drive. This can enhance the reading or output performance of the system, but does not expedite the input or writing process. RAID-3 does use disk striping and also dedicates one drive in the sequence to storing what is known as parity information. This approach is better suited for a single user approach than a multiple user system.

RAID-4 utilizes larger stripes, which makes it easier to read data saved to a particular drive in the sequence. Other redundant array strategies include one or more characteristics of these three examples, and often add additional functions such as a rotating parity array or the ability to read files saved on a single drive in the sequence. The type of redundant array chosen depends a great deal on the size of the data files that must be saved and the number of users that will be allowed to access the collection of drives.

It is important to note that in addition to the nine different types of redundant array strategies, there is one form of redundant array that is not really redundant. Known as RAID-0, this approach does utilize disk striping and does make use of more than one hard drive. However, the data is not duplicated on each drive connected with the system. While this approach does not offer protection against the loss of data due to a primary hard drive failure, striping and using two or more drives does tend to increase the speed of input and output functions.

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