Zend Anwar

RAID stands for Redundant Array of Inexpensive (Independent) Disks.

Please check following levels of RAIDs.

RAID 0 – Striping
RAID 1 – Mirroring
RAID 5 – striping with parity
RAID 10 (also known as RAID 1+0) – combining mirroring and striping

RAID level 0 – Striping
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Minimum 2 disks.
Excellent performance ( as blocks are striped ).
No redundancy ( no mirror, no parity ).
Don’t use this for any critical system.
RAID 0 offers great performance, both in read and write operations. There is no  overhead caused by parity controls.
All storage capacity is used, there is no overhead.
The technology is easy to implement

Disadvantages

RAID 0 is not fault-tolerant. If one drive fails, all data in the RAID 0 array are lost. It should not be used for mission-critical systems.

Ideal use

RAID 0 is ideal for non-critical storage of data that have to be read/written at a high speed, such as on an image retouching or video editing station.

If you want to use RAID 0 purely to combine the storage capacity of twee drives in a single volume, consider mounting one drive in the folder path of the other drive. This is supported in Linux, OS X as well as Windows and has the advantage that a single drive failure has no impact on the data of the second disk or SSD drive.

RAID level 1 – Mirroring
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Minimum 2 disks.
Good performance ( no striping. no parity ).
Excellent redundancy ( as blocks are mirrored ).
RAID 1 offers excellent read speed and a write-speed that is comparable to that of a single drive.
In case a drive fails, data do not have to be rebuild, they just have to be copied to the replacement drive.
RAID 1 is a very simple technology.

Disadvantages

The main disadvantage is that the effective storage capacity is only half of the total drive capacity because all data get written twice.
Software RAID 1 solutions do not always allow a hot swap of a failed drive. That means the failed drive can only be replaced after powering down the computer it is attached to. For servers that are used simultaneously by many people, this may not be acceptable. Such systems typically use hardware controllers that do support hot swapping.

Ideal use

RAID-1 is ideal for mission critical storage, for instance for accounting systems. It is also suitable for small servers in which only two data drives will be used.

RAID 5 – striping with parity
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Minimum 3 disks.
Good performance ( as blocks are striped ).
Good redundancy ( distributed parity ).
Best cost effective option providing both performance and redundancy. Use this for DB that is heavily read oriented. Write operations will be slow.
Read data transactions are very fast while write data transactions are somewhat slower (due to the parity that has to be calculated).
If a drive fails, you still have access to all data, even while the failed drive is being replaced and the storage controller rebuilds the data on the new drive.

Disadvantages

Drive failures have an effect on throughput, although this is still acceptable.
This is complex technology. If one of the disks in an array using 4TB disks fails and is replaced, restoring the data (the rebuild time) may take a day or longer, depending on the load on the array and the speed of the controller. If another disk goes bad during that time, data are lost forever.

Ideal use

RAID 5 is a good all-round system that combines efficient storage with excellent security and decent performance. It is ideal for file and application servers that have a limited number of data drives.

RAID 10 – combining mirroring and striping
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Minimum 4 disks.
This is also called as “stripe of mirrors”
Excellent redundancy ( as blocks are mirrored )
Excellent performance ( as blocks are striped )
If you can afford the dollar, this is the BEST option for any mission critical applications (especially databases).
If something goes wrong with one of the disks in a RAID 10 configuration, the rebuild time is very fast since all that is needed is copying all the data from the surviving mirror to a new drive. This can take as little as 30 minutes for drives of  1 TB.

Disadvantages

Half of the storage capacity goes to mirroring, so compared to large RAID 5  or RAID 6 arrays, this is an expensive way to have redundancy.

What about RAID levels 2, 3, 4 and 7?

These levels do exist but are not that common (RAID 3 is essentially like RAID 5 but with the parity data always written to the same drive). This is just a simple introduction to RAID-systems.