|Redundant Array of Inexpensive (or Independant) Drives.
RAID refers to a data storage device that incorporates a group (or an array) of disk drives that are joined together for a particular purpose.
This joining can be done by either hardware or software.
However the reason for it is because certain functions (ie. applications or user requirements) are so large that a single hard drive alone cannot perform that function.
RAID is basically when 2 or more drives work together as one big drive.
RAID has various levels depending upon the application environment and how critical the functions performed are. Here are some explainations about the various levels of RAID.
|RAID level 0 requires a minimum of 2 drives to implement.
RAID 0 implements a striped disk array: the data is broken down into blocks and each block is written to a separate disk drive.
|RAID 0 is easy to implement and the I/O performance is greatly improved by spreading across many channels and drives.|
|RAID level 1 requires a minimum of 2 drives to implement.
RAID 1 implements disk mirroring where a copy of the same data is recorded onto two sets of striped drives.
|In this situation when data loss occurs on one disk, the second disk can kick in and take over. There is no need to rebuild the system.|
|RAID level 0+1 requires a minimum of 4 drives to implement.
RAID 0+1 implemented as a striped array whose segment are RAID 1 arrays.
If more than 2 hard disks are chosen for RAID 1, RAID 0+1 will be performed automatically.
|RAID level 3 requires a minimum of 3 drives to implement.
RAID 3 breaks data into logical blocks, the size of an IDE disk block, and then stripes these blocks across several drives. One drive is dedicated to parity. If a disk fails then the original data can be reconstructed from the parity information.
|RAID level 5 requries a minimum for 3 drives to implement.
Each entire data block is written on a data disk; parity for blocks in the same rank is generated on Writes, recorded in a distributed location and checked on Reads.