RAID stands for – Redundant Array of Inexpensive Disks. Well It used to be known as that but It is now commonly known as Redundant Array of Independent Disks.
“a data storage virtualisation technology that combines multiple physical disk drive components into a single logical unit for the purposes of data redundancy, performance improvement, or both.” – Wikipedia
To put it simply it is a way of strapping multiple drives together to work as one big drive. It can be used to provide fail over so that if one drive fails its counterpart will take its place until the failed drive is replaced or it can be used to increase performance by having the same data on multiple drives to increase the read times.
As to be expected each different type of raid has its own perks. Here is a quick look into each of them.
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RAID 0 is also known as striping. It splits the data between all the present drives. It doesn’t how ever have any parity or backup so if one of the drives fails then the data is lost. As RAID is a collection of drives the minimum amount of drives that can be used for RAID 0 are 2.
Due to the fact that there is no redundancy it is highly recommended that you don’t use RAID 0 for important data. The main objective of RAID 0 is speed, It is the quickest of the group but the riskiest. This ratio of reliability and speed makes this a common go to setup for gaming rigs.
RAID 1 is essentially a mirror and every drive has a partner. This a more reliable set up because you have two sets of all the data. With there being two sets of the same data there is an increased read time but a decreased write time.
The “partner” system of RAID 1 means that the amount of drives that can be used has to be a multiple of 2.
RAID 5 is a single parity RAID and distributes the parity across drives. The blocks are striped like in RAID 0 but the parity allows for the rebuild of drives if one fails. It is a very common RAID that is used with NAS’s due to the fact that it stores parity on each drive allowing a failure of 1 drive. If a drive fails then the data can be rebuilt by using the stored data on the other drives. This also makes NAS’s hot swappable for when the drive fails allowing the data to be rebuilt on the new drive from the remaining drives.
RAID 6 is almost identical to RAID 5 in the sense that it stores data on each drive to allow other drives data to be rebuilt upon the event of a drive failure. RAID 6, however, takes it one step further in the sense that it allows 2 drives to fail and be recovered instead of 1.
RAID 10 is a combination of RAID 1 and RAID 0. It has to be a minimum of 4 drives and can only be added to in pairs. Every drive that is added needs a back-up drive to accompany it. The data is striped from the RAID 0 side of it but each drive is mirrored so that data can be recovered in the event of a disk failure.
Due to the fact that the blocks are mirrored and striped and has great performance and great reliability.
You can find a great introduction to RAID at HowToGeek