Hello students today we are going to discuss all about RAID so let us begin with Now, what do you mean by RAID? in most of our systems We are having one hard disk for storing the data if due to any mechanical failure or some disk failure It may be that Hard disk will get corrupt and all our data will get lost. So what could be the solution we could replace a single hard disk with multiple hard drives so what will be the advantage of this, our data will remain secure our data for a longer time. How will you define the RAID? RAID is nothing but Redundant array of inexpensive or independent disks initially it was labeled as inexpensive, but later on industry started using the Norms independent disks. What is the advantage of using this RAID? If for some reason one hard disk is lost then our data loss does not take place. RAID is nothing but a collection of various disk organization techniques. It is used to get better disk performance, reliability or both It could be structured in in many ways. In this tutorial we are going to study from RAID Level 0 to Raid level 6 so let us begin with RAID levels, but prior moving to RAID Level 0 we are going to study one term called as data striping now here you can see Numerous blocks are there. These blocks are nothing but segments of data and we have taken two hard drives All these block of data are going to be stored in these two hard drives. But what we are going to do is that at one particular moment We are going to transfer two blocks of data to these two hard drives. So what will be the benefit of this the reading and writing of the data will be much faster in this scheme This technique is known as Data Striping Once again, I will revise this, Data stripping is nothing but the technique of splitting data for spreading it across multiple hard drives. It could exist at three levels Bit Level, Byte Level and Block Level Remember block is nothing but group of number of bytes RAID level 0 uses Block Level data striping here fault tolerance is none as if one of the hard drive fails. Then our data will get lost What about the performance ?Performance is fastest as parallel operations could be done. What about storage space? Consider both hard drives are of 50GB Then in all total 100 GB could be utilized for storing the data Hence storage space is 100% Next level is RAID level one. It uses a concept called as mirroring. What is mirroring? Mirroring is nothing but copying the same data to another hard drive and what would be the advantage of this? Advantage is that if one hard disk fails then we do have another hard disk on which our data is stored So we could replace the failed hard disk and we could utilise the stored data in the second hard drive, but what about the performance and storage space . Performance will be 50% as we are duplicating the work and storage space out of 100 GB available only 50 GB could be properly utilized another 50 GB is kept only for the mirroring of the data. Next level is RAID level 2. Here as seen in the diagram Bit level Striping is used. What is Bit Level Striping? It consists of splitting the bits of each byte across multiple disks. Here you can see we are utilising 4 Hard Drives for storing the bits of each particular byte. And what is parity ? Parity is the simplest technique for detecting and correcting error. In this level extra disks are used for storing this parity information. This was not implemented accurately and this level is hardly used Next level is RAID level 3 here Byte level striping with parity is used here one extra disk is utilized for storing all the parity information. If one drive fails then the parity bit helps to restore the failed disk, but if the parity Drive fails then data recovery is not possible. Next level is RAID Level 4 Here block-level striping with parity is used Again one entire disk is kept for storing the parity information Here also, if one drive fails then parity Drive helps to restore the failed disk, but if the parity Drive fails recovery of disk is not possible. RAID level 5 uses Block striping but here the major difference is the parity is distributed among Several hard drives as is shown in the diagram. So in case one hard drive fails still the other remaining hard drives can help in restoring the failed hard disk. This level 5 can help to handle one disk failure. This level provides fast performance. But the disadvantage is that the storage space could be utilized only up to 75 percent means one entire hard disk is to be kept for storing the different Parity information at this particular level it cannot handle 2 disk failure Raid level 6 is the enhanced version of RAID level 5 here as is evident from the diagram. We are using parity bits, but we are using double parity bits and they are distributed among several hard disks, so this particular level helps to restore failure of two hard drives successfully which was not possible in the RAID level 5. So this RAID level 6 is mostly utilized in big companies such as Google and Facebook where High availability of data is required So let me conclude what we have studied today RAID is nothing but Redundant array of independent Disks RAID level 0 consists of data striping RAID level one uses the concept of mirroring RAID Level 2 uses Bit level data striping with parity.Raid Level 3 uses byte level data striping with parity RAID level 4 uses Block Level data striping with parity RAID level 5 uses block-level distributed parity bit and lastly the RAID level 6 uses Block Level distributed parity bit but we are using here double parity bits to help us recover failure of two hard disks Thank you for watching and come back for future tutorials.