Basic concepts of RAID

RAID(Redundancy Array of Independent Disk):

A RAID  is an only way in which you can link up  several hard disks so that if any one of them fails, the other one can take over the load

Types of   RAID:

1)Hardware RAID

2) Software RAID

Hardware RAID: It has its own independent disk subsystem and resources.It doesn’t use any resource from the system such as RAM, CPU, and power.Since it has its own dedicated resources it will not put any additional Load on the system, It also provides very high performance.

Software RAID: Performance wise when compared to hardware RAID software RAID delivers slow performance since it uses all the resources from the system.

concept of RAID:

1.Hot spare: This is the additional disk in the RAID array, if any disks fail, data from the faulty disk will be migrated to the spare disk automatically.

2.Mirroring: The copy of the same data will be available on the mirror disk, like making an additional  copy of data

3.Striping: If this feature is enabled then data is written to all the available disks randomly, it is like sharing the data between all disks, so all of them fills quickly.

4.Parity: The parity regenerates the lost data from the saved parity information.

There are different levels of RAID available based on how mirroring and striping needed, Among these levels, LEVEL 0, LEVEL 1, LEVEL 5   are mostly used in Redhat Linux.

Let us have a look at these different levels of RAID

RAID 0-Striping:

It provides striping without parity, Since it doesn’t store any parity data performs the read and write operation equally, Speed would be much faster than other levels, Minimum two hard disks required for this level.All the harddisks in this levels are filled equally.You should use this level only if the read and write speed are concerned.when you decide to use this level always have a backup plan on your data because a single disk failure from the array will result in total data loss.

RAID 1-Mirroring:

In this level it provides parity without striping, data will be written on both the harddisks, if any of these failed or remove still we can get the data.This level requires two hard disks.It means if you want to use two hard disks then you will have to deploy 4 hard disks or if you want to use one hard disk then you will have to use two hard disks, First hard disk stores the original data while the other disks provides the exact same copy of the first disk, performance is reduced since data is written twice,You should use this level only if data is concerned at any cost

RAID 5 Parity with Striping:

This level provides Parity and striping, This level requires minimum 3hard disks.It writes parity data equally in all disks.If anyone of disk fails, then data can be reconstructed from the parity data available on remaining disks.

NOTE: When you are using Hardware RAID  device, use hot swappable hardware RAID device with spare disks, if any disk fails data will be reconstructed on the first available spare disk without any time.

In our next article, I will show you how to configure RAID in Red hat Linux.

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