User manual

ERQ12-U4R2 & ERQ12-F2R2 Serial ATA Disk Array Systems

1 Overview – Understanding RAID

RAID 3

In RAID 3, data is divided into pieces; the parity of these pieces is calculated; and the pieces are

written to separate disks in parallel with the writing of the parity to a dedicated disk. This process

is called striping with parity. The parity disk stores redundant information about the data on other

disks. If a single disk fails, then the data on the other disks is used to regenerate the data on the

failed disk. Striping delivers a high access rate and parity delivers good data availability. The sin-

gle parity disk is a bottleneck on sequential writes, since parity must always be written to the sin-

gle parity disk.

RAID 3 consists of two or more disks used for data and one disk used for fault tolerant data. The

total capacity of RAID 3 is the sum of the capacities of each data disk. Add disks until the desired

capacity is reached, then add one more disk for fault tolerance.

RAID 3 is used by the following applications that request large amounts of data sequentially:

• Processing of graphical or video images

• Processing of CAD/CAM files

RAID 3 has the following distinctive features:

• Excellent performance for data transfer characteristics

• Not well suited for transaction processing or other I/O request intensive applications