Understanding RAID
The term RAID stands for Redundant Array of Independent Disks. RAID technology allows you to group together the storage capacities of two or more disks, and manage them as a single storage unit. Users are unaware that this array is not a single disk. A RAID array is known as a virtual device, since the operating system views it as a single device when storing data.
RAID can either be controlled at the software or the hardware level. If it is hardware controlled, a RAID controller will be supplied. This is a plug-in card that is attached to the motherboard, and the disks are plugged directly into this controller. It controls all RAID activities, so that the motherboard, and the operating system, are not aware that it is anything other than a single disk device. This is a good option for large RAID arrays, since it tends to give better performance.
When using this option, RAID devices are configured into the operating system in exactly the same way as single-unit devices. There are no special configuration considerations.
If RAID is configured at the software level, partitions are grouped together into a virtual device and appear to higher layers of the operating system as a single unit. This gives good performance under Linux, and is a less expensive option.
Depending on how it is used, RAID can have several advantages, including increased performance, better fault tolerance and data integrity, and more efficient storage. RAID levels are a way of defining the actual type of RAID configuration.