RAID = Blazing fast Hard Drive performance

Have you ever had a RAID before?

RAID is a technology used to increase hard drive performance and fault-tolerance.

What is fault-tolerance?

The hard drive inside your computer is responsible for storing programs and user data. RAID performance refers to the time that it takes the hard drive to read and write information; fault-tolerance deals with the means to protect data stored on the hard drive.

RAID is an acronym which stands for Redundant Arrays of Inexpensive (or Independent) Disks.

Generally speaking, the word 'Array' is a techy-term which represents related information formed in a "block". In the case of a RAID array, hard drives are combined to form one physical block (see picture).

RAID-0 through RAID-5

There are five types of RAID array architectures. Each design provides a different method used for redundancy and fault-tolerance, but differ in features and performance. The scope of this article will only deal with RAID-0 and RAID-1 since they are most commonly used in home-based computing.

Why RAID?

The idea of RAID is to combine multiple, inexpensive hard disk drives into an array which yield performance that exceeds that of a single large drive of the same size. Hard drives used in a RAID array appear to the computer as a single unit.

Not all the drives in a RAID array must be identical.

By definition, RAID uses a series of inexpensive drives and combines them as a single unit. However, all units of the array must be the same size. Therefore, the smallest hard drive defines the constant unit size used throughout the array.

For example, an array consisting of 105, 5000, 300, and 110 megabyte hard drives would default to 105 megabytes per unit, yielding a total of 420 megabytes in the array. Additionally, the hard drive with the slowest read and write access times (typically the smallest hard drive) defines the collective transfer speed between all drives. For optimal performance and space utilization, it is best to build an array with identical hard drives.

Capiche?

Hard Drive access compared to RAM access speeds

In data acquisition, a hard drive is much slower in comparison to RAM computer memory and can be a system performance bottle-neck. A typical computer system consists of one hard drive which uses only a single channel of communication to transfer data. On a RAID-0 system which uses multiple channels to transfer information, data is transferred twice as fast. This significantly increases data read and write speeds.

RAID-0

With RAID-0, data is split across all drives, resulting in very high read and write speeds. None of the drives in a RAID-0 array are used to store redundant information, therefore, the failure of any disk in the array results in data loss. This RAID level is commonly referred to as Striping.

RAID-1

RAID-1 provides data redundancy by writing the same information to two or more drives. The performance of a level 1 array tends to be faster on reads and slower on writes compared to a single drive configuration. However, if either drive fails in a level-1 array, no data is lost. This RAID level is commonly referred to as Mirroring.

RAID 0 + 1

Some RAID configurations allow for the combination of RAID 0 + 1, which utilize both methods at the same time. The result is increased system performance, while ensuring data protection through redundancy. Typically, a setup like this would require 4 hard drives of identical size.

Two types of RAID: Hardware and Software

The hardware based RAID controllers are independent of a host computer and present all disks in the array as a single entity. A software driver is required to operate the RAID controller on an operating system and is supplied by the manufacturer.

Software RAID solutions are completely hardware independent. However, they require system memory, consume processor time, and are operating system dependent.

In general, a software RAID does not perform as well as hardware RAID. It can degrade system performance because this type of RAID must contend with other programs which also acquire processor time. This type of RAID is very uncommon.

Uses of RAID

RAID is widely used in audio and video editing, where files are large in size and must be loaded and reloaded during the editing process. Additionally, some operating systems and programs are quite large and require constant hard drive access time. Considering that a hard drive is one of the slowest peripherals used for transferring data inside a computer system, RAID can significantly increase overall system performance.

RAID is becoming more common and is included as a hardware performance solution by some high-end motherboard manufacturers. RAID controllers can also be purchased separately; newer controllers occupy a single PCI (peripheral expansion) slot and may be implemented into existing system configurations.

Hardware RAID controllers can be purchased as an add-on to an existing computer configuration. Two of the best brand names in high-performance IDE* RAID controllers are Adaptec (AAA) and Promise IO. While Adaptec products are sometimes more sophisticated and higher in price, Promise IO offers no-frills, same-level performance and a lower price tag.