RAID technology

RAID technology provides two basic functions:

 Higher I/O performance by striping data over multiple physical disks, and therefore achieving an

even I/O distribution over all disks

 Fault tolerance by mirroring disks or adding parity information

RAID levels 2, 3, and 4 are not as efficient and are not commonly used. For more information about

these levels refer online.

RAID 0 is called disk striping. All read/write operations are split into slices (usually 16-128 KB) that

are spread across all disks in the RAID array. There is no redundancy added. Read and write

performance is improved by equally distributing workload on all participating disks. This level

provides the highest performance of all RAID levels.

In RAID 1, every physical disk is mirrored. All write operations are written to the original disk and

to the disk mirror. Write performance may be a little lower as both disks’ writes must be

synchronized. With mirroring, one disk may fail without data loss.

 In RAID 0+1 (also called RAID 10), every disk in the disk stripe set is mirrored. It provides nearly

the same performance as RAID 0 but adds redundancy at the cost of doubling the number of disks.

RAID 5 combines disk striping with parity. One physical disk is added to hold the parity

information. The parity information is also striped along all disks. Every write operation needs 2

physical reads and 2 physical writes (read data + parity and write new data + new parity). It offers

less fault tolerance, as only one disk in the whole array may fail without data loss. The total disk

storage is not available to store data.. There needs to be enough free space available for parity

information to equal the size of the smallest disk in the array.