Understanding the Concepts of RAID (Redundant Array of Independent Disks)

In this segment, we are going to discuss about RAID.


To guarantee availability in the data center, a kind of data storage innovation called RAID (Redundant Array of Independent Disks) is used. RAID is various storage drives (at least two), hard drives for instance, that are connected together to make one single huge volume of storage capacity. This outcomes in expanded performance as well as data redundancy. There are various types, or as they are normally referred to levels of RAID and relying upon which level of RAID is utilized (i.e. RAID 0, 1, 4, 5, or 10), storage availability and redundancy are accomplished utilizing one or a combination of three strategies; mirroring, striping, and parity.


At the point when the mirroring technique is used, two same-sized drives are connected together and what gets stored in with the first likewise gets stored in with the second, making a precise copy for redundancy purposes. In the figure below, the mirroring technique used by RAID 1 shows that the blocks are similar on both disks.

With the striping technique, the data being written navigates along with the connected drives, so no drives are similar. The connected drives work as one single drive and the data is ‘striped’ between the two as appeared by the RAID 0 model in the picture below. The advantage of striping is that it expands capacity and results in quicker performance since it requires less time to store the data a single time to one disk (for this situation, two disks working as one) than it does to store the data many times to make a duplicate copy on every one of the connected drives, as is done in case of the mirroring strategy. A main point is that if one of the connected drives goes down, all the data/information will be unavailable. So, in the case of RAID 0, the ideal result is the performance, not redundancy. From the outset, this may not appear to be a helpful data storage choice, however, there are a few tasks, for example, visual computerization or media compilation that requires higher performing storage like RAID 0 for just less amount of time.

Mirroring offers redundancy, opposite to striping because, as appeared in the above picture, if one drive goes down, all the information is saved on the other disk. One approach to get the best of both techniques is with a RAID 10 (1+0) or a RAID 0+1 storage setup, which includes both mirroring and striping.

Another RAID strategy, called Parity, is a method for checking if there are errors in a string of data. Parity is used in certain RAID setups by including a data bit at the end of a string of data being written to the disk.

As you may know, data is comprised of 0s and 1s. A parity data bit goes about as an approach to check the number of 1s in the string of data. There are two kinds of approaches to using parity: odd parity and even parity.

01010101 0

The first arrangement of characters 01010101 example data output above is a string. After the string, the last featured character 0 shown above is the parity bit.

The example above is the case of even parity. A parity bit of 0 implies that the number of 1s, including the parity bit, is even. This is affirmed by the four 1s in the string. On the off chance that one of the 1s was inadvertently changed to a 0 during the transmission, the number of 1s including the parity bit would be odd, which becomes incorrect. If the data string doesn’t match the data bit, it implies that there was an error in the transmission of the information or data.

The following would be the case of odd parity:

01010101 1

In the above example, the number of 1s including the parity bit 1, is five and so it is odd.

RAID levels that use Parity, assign one of the disks in the volume as a parity disk where the parity data is stored. The parity data can be used to recover the lost information from the failed disks.


RAID 2, which is not used that much nowadays, stripes information at the bit (instead of block) and uses a Hamming code for error correction. Hamming code is a straight error correction code-named after its creator, Richard Hamming. More information about Hamming Code is HERE.

While it is fascinating and it has its favorable circumstances, we have not found out about any business implementations of RAID 2. Solutions dependent on it were used uniquely in the initial phase of RAID frameworks utilization (before disks were equipped with their very own correction code). Present-day HDDs use different correction and optimization calculations. That is the reason the Hamming framework has begun to be less intriguing in the territory of expert use and it is never again executed in present-day controllers.


RAID 3 functions as RAID 0 does, it uses byte-level stripping, however, it also uses an extra disk in the cluster which is used to store checksums (detecting errors). The read speed is more than good however write speed is not so good – the explanation is the need for checksums calculation.

As can be effectively observed, RAID 3 is not a good option. Along these lines, as it was referenced before, its utilization is uncommon practically speaking. Systems dependent on RAID 3 are for the most part purposed for implementations where few clients refer to the large files.


First, we have to remind you XOR definition:

XOR work result is equivalent to 1 if the two arguments are not the same.

XOR (0, 1) = 1

XOR (1, 0) = 1

XOR work result is equivalent to 0 if the two arguments are the same.

XOR (0, 0) = 0

XOR (1, 1) = 0

Presently let us assume we have 3 drives with the following bits:

1 drive – 101

2 drive – 010

3 drive – 011 

What’s more, we take XOR of that data and place it on the 4th drive.

XOR (101, 010, 011) = 100 { Take XOR of first two drive(101,010) = 111 and then take XOR of result with third drive (111, 011) = 100 (final result)

So the information on the four drives resembles this beneath:

| 101 | 010 | 011 | 100 |

Now, let’s assume that the second drive has failed. At the point when we compute XOR all the rest of the information will be available from the missing drive.

| 101 | 010 | 011 | 100 |

XOR (101, 011, 100) = 010

You can check the missing different drives and XOR of the rest of the information will consistently give you precisely the information of your missing drive.

| 101 | 010 | 011 | 100 |

XOR (101, 010, 100) = 011

What works for 3 bits and 4 drives, works for any number of bits and any number of drives.

This is enough for this section, we have talked about the concept of RAID and the main important RAID levels which are used. If you have any suggestions or thoughts, just comment down below.

Related Concepts:

1. What is Virtualization? Basic Virtualization Understanding Part -1

2. What is a Virtual Machine? Basic Virtualization Understanding Part -2

3. What is Hypervisor and how many types we got here? let’s find out.

4. Know More Deeply on Hypervisor and Virtual Machine.

5. Understanding the Role of Snapshot and Data Centers.

6. Understanding the Computing System Hardware in Data Centers.

Biplab Das

Biplab Das

My name is Biplab Das. I’m a writer, Blogger, Programmer, ICT tutor and a part-time website developer whose childhood obsession with science fiction never quite faded. A quarter-century later, the technology that I coveted as a kid is woven into the fabric of everyday life. I’ve spent the past years to learn these technologies, i recently published a book on computer science fundamentals. People say smartphones are boring these days, but I think everyone is beginning to take this wonderful technology marvel for granted.
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