RAID Full Form

Edited By Team Careers360 | Updated on Jul 14, 2023 10:15 AM IST

What is the full form of RAID?

RAID stands for a Redundant Array of Inexpensive/ Independent Disks. It is a way of storing the same idea in different places. It is the technique of data virtualization that uses multiple hard disks or solid - state drives to provide for data redundancy and performance improvement. This term was coined by David Petterson, Gartha A and Randy Katz In 1988 a case for a redundant array of inexpensive disks (RAID). In this report discussed and established two RAI that could be more resilient and reliable than a single disk

RAID Full Form

Some related key points:

Capacity - given a set of N-Disks each with B blocks. How much availability of user for useful capacity
Reliability - how much can tolerate disks faults
Performance - how good is the response time. How the rate of processing works.
Availability - how availity of the system for actual use that means what fraction of the total session time is a system in uptime mode.

RAID is very transparent about the underlying systems. This means the host system appears as a single bid disk presenting itself as a linear array of black raid allowing older technologies to be by raid without making too many changes in the existing code.

Levels of RAID

The levels of raids are of different types.

RAID-0( striping)

Disk 0	disk1	disk2	disk3
0	1	2	3
1	5	6	7
8	9	10	11
12	13	14	15

Block-0,1,2,3 form a strip
Blocks are striped across the disk

Disk 0	Disk 1	Disk 2	Disk 3
0	3	4	6
1	3	5	7
8	10	12	14
9	11	13	15

Evaluation :

Capacity = N*B

There is no duplication , N disks each having B Blocks are fully utilized. I.e. the entire space is being used to store data.

reliability=0

There is no duplication of data that if we have lost data then we can not be recovered.

RAID- 2 (Mirroring)

Disk 0	Disk 1	Disk 2	Disk 3
0	0	1	1
2	2	3	3
4	4	5	5
6	6	7	7

There are more than one copies of each block and it is stored in a separate disk. Hence, every block has two copies lying on different disks.

Evaluation

capacity=N*B/2

There are only half the space is being used to store data and other half is just a mirror to already stored data

Reliability = 1 to N/2

If one disk fails then it can be handled for certain , because we have duplicates 3 blocks of that disks and if again disk 0 and 2 fail, it can be handled as these blocks of these disks have duplicates on disk 1 and 3. So this is the best case of N/2 disk failure that can be handled.

RAID - 4 ( Block level striping with dedicated parity)

Disk 0	Disk 1	Disk 2	Disk 3	Disk 4
0	1	2	3	P0
4	5	6	7	P1
8	9	10	11	P2
12	13	14	15	P3

In this we adopt a parity - based approach instead of duplication data.
In this one column dedicated to parity.
Parity is calculated using a simple XOR function. For example- if the data bits are 0,0,0,1 the parity bits are XOR(0,0,0,1)=1. In a simple way it is that the even number of ones results in parity 0, and odd numbers of ones results in parity 1

C1	C2	C3	C4	Parity
0	0	0	1	1
1	1	1	0	0

For example if C3 is lost due to some disk failure.

Evaluation

Capacity = (N-1)*B

In this one disk in the system is reserved for storing the parity, hence (N-1) disk are made available for data storage and each disk having b blocks

Reliability =1

In this raid-4 allows recovery of at most 1 disk failure. If more than one disk fails then there is no way to recover the data.

RAID - 5 (Block level striping with distributed parity)

Disk 1	Disk 1	Disk 2	Disk 3	Disk 4
0	1	2	3	P0
5	6	7	P1	4
10	11	P2	8	9
15	P3	12	13	14
P4	16	17	18	19

In this figure parity bit rotates.
This is slightly different from the raid-4 system.

Evaluation

capacity= (N-1)*B

(N-1) disk available for data storage, each disk has B blocks.

Reliability = 1

This allows recovery of at most a disk failure and if more than one disk fails then there is no way to recover the data that’s why we can say this is identical to RAID-4 .

Characteristics of RAID

RAID has multiple systems because there are six different RAID levels and each raid provides unique features.
RAID has multiple storage techniques because different levels have different storage techniques like mirroring striping.
RAID has multiple disks.
RAID has data redundancy and its help copies the same data kept in multiple disks for disaster management.

Advantages and Disadvantages of RAID

Advantages:

Security of data
Corrections of error
Redundant data
Data access speed
Simultaneously 1/0 request

Disadvantages

It is more costly than the SLED system.
Raid systems do not use mirroring are vulnerable to the same data loss
If raid will not be used properly then the overall performance of the system may decrease.
Raid has complex technology
Raid has so many levels with each having some drawbacks so it's tough to choose a raid level.