Century IT blog

RAID (redundant array of independent disks)

July 2nd, 2012

What is RAID?

To answer it shortly, RAID stands for Redundant Array of Inexpensive/Independent Disks.


This doesn’t really answer the question though, because if you look into it a bit more, it’s easy to see that there is more to RAID than first meets the eye.


RAID comes in different levels, ranging from RAID 0 all the way to RAID 10. Although RAID levels 8 and 9 do not exist. Each of these RAID levels work in a different way to each other. I will go over how RAID levels 0, 1, 5 and 10 (RAID 10 also known as RAID 1+0 or 0+1).






RAID 0 is largely used to increase the performance and speed from a collection of hard disks. It works by striping data across the disks, sharing the data as if the two disks were just one. The major downside to this particular level of RAID, is that if one disk goes down, then you have lost all of the data even though one or more disks may still be perfectly healthy. This is no different however, to just having a single hard disk in your computer failing, causing you to lose whatever data was stored on it should you not have backed it up.








The next level of RAID, is RAID 1. This works differently as it mirrors the data across however many disks are in the RAID, creating an exact copy on each disk. This is of course very useful should you store important data across this RAID setup, as if one of the disks were to fail, then you would have lost no data at all, as one of the other disks in the array will still have an exact copy of the data.

This array is only as large as the smallest disk in the array. This means that if you have two 500GB drives and a 250GB drive in the array, the RAID will only be 250GB, disregarding the remaining space left on the two 500GB drives.





The next level of RAID to look at is RAID 5. This type of array is one of the most popular as it provides good performance, good fault tolerance and allows for high storage amounts as well as having an exceptional read speed. Writing speed to the array however does suffer a fair amount so is not the best choice for a write intensive application, though if the array was used to host a database, RAID 5 would be an almost perfect choice.






Finally, there is RAID 10. Also known as RAID 1+0 or 0+1, this particular level of RAID array is generally regarded as the best. On the downside, it is also the most expensive form of RAID array to set up due to the fact that a minimum of 4 disks must be used. The reason behind RAID 10 being called either RAID 1+0 or 0+1, is because it’s simply a combination of RAID 1’s best features and RAID 0’s best features. This means that the data is both mirrored across drives as well as being striped leading to both very quick read speeds as well as fast write speeds. If you can afford to set up a RAID 10 array, then it is definitely the one to go for as it also allows for disk failures without loss of data.




Hot Spare 

In the unfortunate event that a disk should fail in the array, you can also include what are called “Hot Spare” drives. These drives sit idle and unused until the failure of one of the disks in the array occurs. When one does, the Hot Spare drive then becomes active as it is then included as part of the array in place of the disk that was lost.




The above explanations try to clarify what RAID is and identify the benefits of each level of RAID. The subject of computer hardware specifications and the specifics of the types of disks and RAID levels available can be confusing and we would encourage you take advice from an I.T Expert before deciding upon the hardware specfication of a replacement server.


We offer FREE, confidential,  no obligation advice, so why not give us a call.



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