What is RAID?

RAID is an acronym for Redundant Arrays of Inexpensive Disks

There are many applications, particularly in a business environment, where there are needs beyond what can be fulfilled by a single hard disk, regardless of its size, performance or quality level. Many businesses can't afford to have their systems go down for even an hour in the event of a disk failure.

This situation require the traditional "one hard disk per system" model be set aside and a new system employed. This technique is called Redundant Arrays of Inexpensive Disks or RAID. ("Inexpensive" is sometimes replaced with "Independent", but the former term is the one that was used when the term "RAID" was first coined by the researchers at the University of California at Berkeley, who first investigated the use of multiple-drive arrays in 1987.)

The fundamental principle behind RAID is the use of multiple hard disk drives in an array that behaves in most respects like a single large, fast one. There are a number of ways that this can be done, depending on the needs of the application, but in every case the use of multiple drives allows the resulting storage subsystem to exceed the capacity, data security, and performance of the drives that make up the system, to one extent or another.

What is RAID1 data mirroring?

Mirroring is one of the two data redundancy techniques used in RAID (the other being parity). In a RAID system using mirroring, all data in the system is written simultaneously to two hard disks instead of one; thus the "mirror" concept. The principle behind mirroring is that this 100% data redundancy provides full protection against the failure of either of the disks containing the duplicated data. Mirroring setups always require an even number of drives for obvious reasons.

The main advantage of mirroring is that it provides not only complete redundancy of data, but also reasonably fast recovery from a disk failure. Since all the data is on the second drive, it is ready to use if the first one fails. Mirroring also improves some forms of read performance.

RAID Mirroring

Block diagram of a RAID mirroring configuration.
The RAID controller duplicates the same information onto each of two hard disks.

Why do I need it?

RAID Benefits (complete data protection).

Higher Data Security: Through the use of redundancy, RAID provides protection for the data stored on the array. This means that the data on the array can withstand even the complete failure of one hard disk without any data loss.

Fault Tolerance: RAID implementations that include redundancy provide a much more reliable overall storage than can be achieved by a single disk. This means there is a lower chance of the system as a whole failing due to hardware failures.

How much does RAID Cost?

The main disadvantage of RAID mirroring is expense: that data duplication means half the space in is "not used" so you must buy twice the capacity that you want to end up with in the array.

The implementation of RAID also requires additional hardware which is very expensive.
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