#3 Computer Storage

RAID

On servers and high-end PC workstations (such as those used for high-end video editing), at least two hard disks are often linked together using a technology called RAID. This stands for "redundant array of independent disks" (or sometimes "redundant array of inexpensive drives"), and stores the data in each user volume on multiple physical drives.

Many possible RAID configurations are available. The first is called "RAID 0". This divides or "strips" the data in a storage volume across two or more disks, with half of each file written to one disk, and half to another. This improves overall read/write performance without sacrificing capacity. So, for example (as shown above), two 1TB drives may be linked to form a 2TB array. Because this virtual volume is faster than either of its component disks, RAID 0 is common used on video editing workstations.

In contrast to RAID 0, "RAID 1" is primarily intended to protect data against hardware failure. Here data is duplicated or "mirrored" across two or more disks. The data redundancy so created means that if one physical drive fails there is still a complete copy of its contents on another drive. However, this does mean that drive capacity is sacrificed. For example (as shown above), a 1TB RAID 1 volume requires two 1TB disks. While data write performance is not improved by using RAID 1, data read times are increased as multiple files can be accessed simultaneously from different physical drives.

If more than two drives are used, several other configurations become possible. For example, using three of more drives, "RAID 5" strikes a balance between speed and redundancy by stripping data across two drives but also writing "parity" data to a third. Parity data maintains a record of the differences between the blocks of data on the other drives, in turn permitting file restoration in the event of a drive failure. Many modern personal computer motherboards permit two SATA hard disk drives to set up in a RAID configuration. However, for users who do not require the extra speed provided by RAID 0, RAID 5 or RAID 10, there are relatively few benefits to be gained. Not least, it needs to be remembered that any hardware setup featuring more than one internal hard disk -- whether or not in a RAID configuration -- at best provides marginal improvements in data security and integrity. This is simply because it provides no more tolerance to the theft of the base unit, nor to power surges or computer power supply failures (which can simply fry two or more hard drives at once rather than one).

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source : explainingcomputers.com