22Sep RAID

RAID is an abbreviation used for Redundant Array of Inexpensive Disks. RAID was introduced to take conventional disks in the system and club them together parallel. These disks are low cost in high volumes and good reliability to extreme conditions. The host adapter (frequently called a controller in RAID systems) sits between one high-rate data stream (on the computer side) and several lower-rate streams (on the disk side). When the computer writes to the disk, the host adapter takes high-rate data and breaks it into multiple synchronized streams, one for each disk, in a process called striping. Reads by the computer cause the host adapter to take a data stream from each disk, multiplex the set of streams into one stream, and send that resulting stream on to the computer. The one high-speed stream splits into four separate disk data streams at one-fourth the rate of the combined stream.

Do you know RAID can even be used error detection in the storage? A RAID controller can also insert error correction codes. In an eight-disk RAID system, for example, you can add a ninth disk to hold nothing but error correction information. Any of the disks in a system built that way can fail without loss of data. When you replace the failed disk, most RAID controllers can reconstruct the contents of the disk from the surviving ones. Until that process is complete, however, your data is vulnerable to a second failure. Nor does RAID eliminate the need for backup.