RAID products are computer hardware components and modules that use a redundant array of independent or inexpensive disks (RAID) to store the same data in different places on multiple hard drives in order to improve speed, performance and data recoverability. There are several types of RAID products. RAID controllers are computer boards or standalone modules that use special protocols to control RAID disc arrays, groups of storage discs that function as single, large and fast disk drives. Bus-based RAID controllers are connected to RAID arrays and installed on personal computers (PCs) and servers. They are interfaced to RAID arrays via small computer system interface (SCSI), integrated drive electronics (IDE), or advanced technology attachment (ATA) protocols. Integrated RAID controllers are built into the computer motherboard and function like a bus-based add-in card. External RAID controllers are separate devices for higher-end systems. Unlike bus-based RAID controllers, external RAID controllers are removed completely from the larger system. They are housed in a separate hardware structure (box) and use SCSI to present the logical drives of the array to the server.
RAID products support many different RAID levels. RAID 0 or “striping” is non-redundant and splits data across hard drives. The failure of any disk in the array results in complete data loss. RAID 1, known as “mirroring with two hard drives” provides redundancy by duplicating all data from one drive to another. RAID 2 uses hamming codes and is designed for drives that do not have built-in error detection. RAID 3 stripes data at the byte level across several drives, with parity stored on one drive. By contrast, RAID Level 4 stripes data at the block level. The parity information allows recovery from the failure of any single drive. RAID 5 is similar to RAID 4, but distributes parity among the drives. In other words, no single disk is dedicated to parity. RAID 10 combines RAID 0 striping and RAID 1 mirroring across multiple drive groups. RAID 30 stripes data across multiple drive groups and encodes individual drives with rotated XOR redundancy. Sometimes referred to as “just a bunch of drives”, JBOD is type of RAID in which each drive is operated independently, like a normal disk controller. RAID products that use other RAID levels are also available.
RAID products provide both a disk channel interface and a host interface. Disk channel interfaces use SCSI, ATA, IDE, ATA/IDE variants, or fibre channel. Common ATA/IDE variants include serial ATA (SATA), parallel ATA (PATA), ATA-2, ATA-3, ATA/66, ATA/100 and Ultra-ATA. Fibre channel technology uses optical fibers to connect computers and peripheral devices that require high bandwidth. It functions via a serial data transfer architecture that is compatible with SCSI. The most prominent fibre channel standard is arbitrated loop (FC-AL), which can support full-duplex data transfer rates of 100 MBps. Host interfaces for RAID products use fibre channel or SCSI as well as universal serial bus (USB), peripheral component interconnect (PCI), and IEEE 1394. Peripheral component interconnect (PCI) is a local bus system designed for high-end computer systems. 32-bit PCI is a 32-bit bus that supports rates of 33 MHz. 64-bit PCI is a 32-bit bus that supports rates of 66 MHz. IEEE 1394, a standard developed by the Institute of Electrical and Electronic Engineers (IEEE), is also known as FireWire®, a registered trademark of Apple Computer, Inc.