Disk Array controller Part 1
RAID Recovery - Disk Array controller
A disk array controller (DAC) controls the physical disk drives. Each DAC detects whether the respective drive it is connected to is an ATA drive or SCSI drive and communicates with that drive using appropriate protocol. DAC preferably supports Serial ATA and Serial Attached SCSI interface specification.
ATA RAID controller
A simple disk array controller implements hardware Redundant Array of Independent Disks (RAID). It may be fit inside a computer, either as a PCI expansion card, or it can be directly built into the motherboard. This type of controllers also provides the functionality of host bus adapter (HBA). Hence they are also called RAID controllers.
Nowadays, disk array controllers are located in physically independent enclosures, such as disk arrays placed in a storage area network (SAN) or network-attached storage (NAS) servers.
Disk Array Controller with Automated Processor
The disk drive controllers are connected to a microcontroller and an automated coprocessor. The coprocessor accesses system memory and a local buffer. Disk drive controller responds to controller commands from microcontroller by accessing the respective drives, and sends packets to coprocessor. These packets carry I/O data in both directions. It also carries transfer commands and target addresses used by the coprocessor to access the buffer and system memory. The packets can also carry special completion values and I/O request identifiers that detect the completion of processing of each I/O request.
Using round robin arbitration protocol, the coprocessor grants the packet-switched bus to the disk drive controllers. This protocol guarantees a minimum I/O bandwidth to each disk drive and it is greater than the sustained transfer rate of each disk drive. As a result all drives of the array operate at the sustained transfer rate and avoid any possible bottlenecks.
