Using RAID
Redundant Array of Independent Disks (RAID) is a term used to describe the technique of improving data availability through the use of arrays of disks and various data-striping methodologies.
Disk arrays are groups of disk drives that work together to achieve higher data-transfer and I/O rates than those provided by single large drives. An array is a set of multiple disk drives plus a specialized controller (an array controller) that keeps track of how data is distributed across the drives. Data for a particular file is written in segments to the different drives in the array rather than being written to a single drive.
Arrays can also provide data redundancy so that no data is lost if a single drive (physical disk) in the array should fail. Depending on the RAID level, data is either mirrored or striped.
Subarrays are contained within an array subsystem. Depending on how you configure it, an array subsystem can contain one or more sub-arrays, also referred to as Logical Units (LUN). Each LUN has its own characteristics (RAID level, logical block size and logical unit size, for example). From the operating system, each subarray is seen as a single hdisk with its own unique name.
RAID algorithms can be implemented as part of the operating system's file system software, or as part of a disk device driver (common for RAID 0 and RAID 1). These algorithms can be performed by a locally embedded processor on a hardware RAID adapter. Hardware RAID adapters generally provide better performance than software RAID because embedded processors offload the main system processor by performing the complex algorithms, sometimes employing specialized circuitry for data transfer and manipulation.