Redundant Array of Independent Disks (RAID) is a group of hard drives, controller cards, and software to increase the reliability and redundancy of data storage on hard drives. RAID comes in multiple configurations, offering enhanced performance and/or better data reliability. Data is distributed across the drives in one of several ways called ‘RAID levels’, depending on the level of redundancy and performance required.
RAID numbers are allocated according to the required protection or reliability level required, RAID-5 for example, is not representative of the number of drives involved. The most common RAID implementations are 0, -1, and 5. RAID can be implemented with and without the ability to hot-swap a drive.
RAID 0 - The data is written across multiple drives to improve access performance. There is no data redundancy. For example, a 4Meg file would be written across 4 drives in 1Meg pieces. Note that the failure of one drive will render the data inaccessible. The advantage is a much higher throughput.
The RAID numbers are, click on each for its meaning:
Almost all manufacturers provide a diverse of plug-in controllers that allow RAID execution. These controllers interface with SCSI drives and are available in ISA (Industry Standard Architecture) and PCI (Peripheral Component Interconnect) configurations, the highest throughput is via the PCI format. RAID support for IDE drives is not generally available.
All SCSI drives can be used with a RAID controller, and different drive manufacturers' sizes and throughputs can be used on the same bus. Controller manufacturers provide additional information on expectations. RAID controllers can also act as generic drive controllers interfacing to CD, DVD, and Tape Drives and external accessories like Scanners.
RAID drives either be permanently mounted in a chassis, mounted in external drive bays, or externally using Hot-swappable enclosures that each hard drive can be installed or removed without powering down the host computer. eSATA, FireWire, and USB are examples of interfaces that are hot-swappable on computers.
Full RAID protection can be realised even in non-removable drive situations where the RAID system provides data protection and time to take the system off-line to replace a failed drive. This can certainly be a less expensive and potentially more reliable option in place of using expensive removable drive carriers.