RAID means redundant array of independent

disk. It is a type of storage technology. It

combines multiple disk component into a logical

unit. Data is distributed across several RAID

levels.

Redundant array of independent disk is a

category of disk drives that has two or more

drives in combination for fault tolerance. These

are frequently used in the server. It allows you

to store data in the multiple places (redundantly)

to improve the storage performance.

In the 1987 David Patterson, Garth Gibson and

Randy Katz first published their research paper.

Their paper name was “ A case of Redundant

Arrays of Inexpensive Disks”. Which helps to

form the modern RAID industry. Their paper

defined 1 to 5 RAID levels. Today more levels

are defined. This technology remains vibrant as

ever.

Number of standard schemes are evolved those

are refer as levels. Originally there ware five

levels but today it vibrantly evolved more levels.

It’s level and original data format is standardize

storage networking industry association (SNIA).

RAID means redundant array of independent

disk. It is a type of storage technology. It

combines multiple disk component into a logical

unit. Data is distributed across several RAID

levels.

Different architecture are provided by RAID

followed by each architecture provides

performance, capacity and tolerance. These

levels are 0, 1, 2, 3, 4, 5 and 6.

Provides data striping (spreading out files across

multiple disk drives) but without redundancy. It

highly improves the performance. In certain case

if one drive is fail then all data is lost. Data is

fragmented is called blocks. Number of block is

dedicated to the stripe size. It is configuration

parameter of array. Block is written in the same

sector simultaneously in the different drives.

Level 1 provides the twice the read transaction

rate in the same disk. Write transaction rate is

also same. Write request update the stripe of

both drives. The array is continue to operate as

long as at one drive is operating. It has separate

controller in each drive for simultaneously reads

called multiplexing.

Strip data at the bit level rather than the block

level. In this level all disk spindle rotating in a

synchronized way that each sequential bit on a

different drive. Across these bits hamming code

is calculated.

It provides byte level striping with a dedicated

parity disk. It can’t service simultaneously it is

used rarely. Parity is calculated and stored in the

dedicated parity drive.

Commonly used implementation of RAID is

block level striping with a dedicated parity disk.

If disk fails then parity create a replacement.

Disadvantage of it creates bottleneck.

It provides data striping at the block level. It

performs excellently in the good fault tolerance.

It requires data and all drives but one to be

operate. Array is not destroyed in a single disk

failure. In a single disk failure it reduce the

entire performance. RAID 5 requires at least

three disk.

It is similar to RAID 5 except instead of one

parity block per stripe. With two independent

parity block RAID 6 can survive loss of two in

among the group of disk.

RAID concept is present from in 1986 and it is

installed in the million of configuration. It lacks

of the standard. RAID implementation is

proprietary and unique to every vendor.

RAID is implemented in the server by a software

called JBOD (just a bunch of disks). It acts as a

logical volume manager it manage the parity

calculation.

These are the cards that can be added to a

server and performs the offload of overloaded

RAID CPU. It is a better solution for a single

server. For managing the mirror data it CPU

spend no processing power. It uses either

internal drives or JBOD.

It consist of two high performance and

redundant RAID controller. They support

multiple RAID levels and different drive types

and speeds. Storage array also have snap shot,

volume copy etc. There are different types of

RAID controller like IBM RAID controller.

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