Revolutionary Data Storage Solution: RAID

The Revolutionary Data Storage Solution: RAID

Alternative Title: RAID: Superior Data Storage Capacity

Meta Title: Reliable RAID Solutions For Your Data Storage Problems

Alternative Meta Title: A List Of Best RAID Options To Choose From

Meta Description: RAID or Redundancy Of The Independent Disk is the latest solution to data storage issues associated with single disk storage problems. Here is a list of RAID options for you to choose from.

 

Introduction

In this fast developing world of technology, gone are those days when users relied on single disk drives to store data. With the increased use of data storage comes a need to use multiple disk drives or any other mechanism which enhances storage capacity. What you need today are better, faster and safer storage options. Here is a range of RAID levels discussed to enable you to pick the most suitable one for yourself.

 

What is RAID?

Raid is an acronym for Redundancy Array of the Independent Disk. Originally the term was meant for Redundancy Array of Inexpensive Disk. It enables you to have access to multiple secondary storage devices compared to similar older devices having a single disk drive. In layman terms, this technology uses many disks to ensure good performance, more storage capacity and deal with storage faults. This saves you in case one or more drive failures.

 

RAID Technology

Firstly all the 7 levels of Raid technology contain a set of drives. These multiple disk drives are considered as a single logical disk by the Operating System. Secondly, the disk drives in the RAID group store data thus enhancing storage capacity. Parity information is stored in the multiple disks. In case of a disk failure, data is recovered from the parity information. These levels use techniques like stripping and mirroring and parity disk to help with storage issues.

Various Levels of RAID

RAID 0

This level uses the stripping technique where data is sent to the multiple disks. Here the data is broken into small parts and then distributed to all the disks in the array. It enhances performance by accessing multiple disks simultaneously. In case of a single disk failure, all data is lost.

Example:

Disk 0

Disk 1

Disk 2

Disk 3

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

 

In the above table, block 0, 1, 2,3 are a stripe.

Now in this level, we place the stripped data as shown below

Disk 0

Disk 1

Disk 2

Disk 3

15

17

19

21

16

18

20

22

23

25

27

29

24

26

28

30

 

In the table above there is no mirroring of data hence, we lose the data in case of disk failure.

Pros

  • Various data requests do not put a burden on the same disk, resulting in greater output.
  • It enhances performance and is considered the best among all levels in this respect.
  • It can work with even 2 drives.

Cons

  • The biggest problem with this level is that you lose all the data in case of a single disk failure.
  • It fails to detect an error.
  • It does not fulfill the purpose of RAID technology due to lack of fault tolerance.

 

RAID 1

This level uses what is called ‘mirroring of data’. This means it uses its multiple disks to store exactly the same content through duplication of data. You could also say it uses half of the available space to store an exact copy of the data.

Example:

Disk 0

Disk 1

Disk 2

Disk 3

S

S

T

T

U

U

V

V

W

W

X

X

Y

Y

Z

Z

 

In the above table, there is duplication of data. Hence only half of the space is utilized to store data.

Pros

  • It provides 100% redundancy thus making the system fault tolerant.
  • In case of a single drive failure, you have your data safely stored in the other drive.
  • This also means the RAID drive group will function even in case of a single drive failure.

Cons

  • Here the stored data will use double space, because of mirroring or duplication of data. So it enables us to actually use only half of the storage capacity.
  • As any data here requires twice the amount of storage so it turns out to be expensive.

 

RAID 2

RAID 2 is rarely used. This level stripes data at a bit level and each bit is stored in a separate drive. It requires a disk separately for storing ECC code of data. The level uses the Hamming code for error correction. You would agree that it is complex and expensive.

Pros

  • It uses a selected drive for uniformity in storing data.
  • It detects error through hamming code.
  • It can be a good answer to data-security problems.

Cons

  • It uses an extra drive for error detection.
  • The need for hamming code makes it inconvenient for commercial use.

RAID 3

The RAID 3 level stripes data at the byte level. It requires a separate parity disk which stores the parity information for each byte. When a disk fails, data can be recovered with the help of parity bytes corresponding to them. Then the retrieved data can be stored in a new disk. It also has a high read speed.

Example:

Disk 0

Disk 1

Disk 2

Disk 3

M

N

O

P (M, N, O)

R

S

T

P (R, S, T)

U

V

W

P (U, V, W)

X

Y

Z

P (X, Y, Z)

 

Pros

  • It enables high-speed transmission of data.
  • In case of a disk failure, data can be reconstructed using the corresponding parity byte.
  • Data can be used parallelly.
  • It might be used where few users are referring to large files.

Cons

  • It needs an extra file to store parity bytes.
  • Its performance is slow in case of files of small size.
  • It can be said that it is not a reliable or cheap solution to storage problems.

 

RAID 4

RAID 4 is a quite popular one. It is similar to RAID 1 and RAID 3 in a few ways. It goes for a block level data stripping which is similar to RAID 0. Just like RAID 3, it uses parity disk to store data. When you combine both these features together you will clearly understand what RAID 4 does. It stripes data at the block level and stores its corresponding parity bytes in the parity disk. In case of a single disk failure, data can be recovered from this parity disk.

Example:

Disk 0

Disk 1

Disk 2

Disk 3

M

N

O

P 0

R

S

T

P 1

U

V

W

P 2

X

Y

Z

P 3

 

Using the above table, parity can be calculated by XOR (function).

T1

T2

T3

T4

Parity

0

1

0

0

1

0

0

1

1

0

 

If T4 is lost then we can recover it from parity bit and other columns.

Pros

  • In case of a single disk failure, the lost data is recovered from the parity disk.
  • It can be useful for large files.

Cons

  • It does not solve the problem of more than one disk failure.
  • The level needs at least 3 disks as well as hardware backing for doing parity calculations.
  • It might seem to be slow in case of small files.

RAID 5

RAID 5 is one of the most popular ones especially for a system with three or more drives. This level has some similarity with RAID 4. This level too uses the parity but in a distributed way. It stripes data across all drives in a somewhat rotating way. It stripes data at the byte level.

Example:

Disk 0

Disk 1

Disk 2

Disk 3

Disk 4

10

11

12

13

P0

15

16

17

P1

14

20

21

P2

18

19

25

P3

22

23

24

P4

26

27

28

29

 

The table above shows the rotation of parity bits.

Pros

  • This level is known for distributed parity among the various disks in the group.
  • It shows good performance without being expensive.
  • It uses only one-fourth of the storage capacity for parity and leaves three-fourths of the capacity to be used for storing data.

Cons

  • The recovery of data takes longer due to parity distributed among all disks.
  • It is not able to help in the case where more than one disk fails.

RAID 6

RAID 6 is also known as double-parity RAID. It is an enhanced version of RAID 5. It stripes data at block level and stores two corresponding parity block on all disks. First, it does stripping of data and follows it up with mirroring of data. In other words, you could say first it works like RAID 0 for stripping and then RAID 1 in mirroring.

Example:

Disk 1

Disk 2

Disk 3

Disk 4

J 0

K 0

Q 0

P 0

J 1

Q 1

P 1

M 1

Q 2

P 2

L 2

M 2

P 3

K 3

L 3

Q 3

 

Pros

  • It can help you in case of 2 simultaneous disk failures.
  • The number of drives for this level should be an even number with a minimum of 4 drives.

Cons

  • It uses only half for storing data as the other half is used for mirroring.
  • It needs two extra disks for parity.
  • It needs to write in two parity blocks and hence is slower than RAID 5.
  • It has inadequate adaptability.

 

Conclusion

There are a number of other RAID levels too. Some of them are RAID 10, RAID 5EE, RAID 50, RAID 60. Different RAID level is a combination of different qualities. Each level can be judged on the basis of redundancy, read performance, writing performance, minimum disks required and usage of the disk drive. The best RAID level for you depends on your storage space as well as performance and reliability you are looking for. Generally, a number of drives result in better performance. Each RAID level has its own set of advantages and disadvantages. So you have to decide what you are looking for is safety or speed or storage space.

 

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