Everything You Ever Wanted To Know About RAID But Were Afraid To Ask

Posted on Dec 5 2014 - 7:49am by Editor

To some people, RAID is a brand of chemical spray used to kill ants and roaches. But in the computer world, RAID is something completely different! In case you wondered, RAID stands for “Redundant Array of Inexpensive Disks.”

RAID is an acronym that’s used by IT experts and systems builders alike for many generations now. On first reflection, RAID seems to be something to do with data storage. Of course, you are quite right!

Still, if you know little to nothing about RAID, this blog post will tell you everything you need to know about the topic. Do you want to learn more about computers in general? Perhaps you want to learn more about advanced topics? Keep reading to increase your IT knowledge!

RAID arrays

What is RAID?

Different people have different requirements when it comes to data storage. For instance, some folks want to ensure they minimize the amount of times any data loss occurs. Whereas others want to have plenty of storage space if they work with large files.

And, for some people, speed of data access is essential in certain applications. RAID offers plenty of helpful solutions to those needs and more. It’s important to note that RAID doesn’t offer solutions to all problems though.

RAID is good at protecting against data loss from failing hard drives. But it won’t help you if you delete a file and want to recover it somehow. For that, you need to use specialist RAID data recovery services companies.

The way that RAID works is quite straightforward. Using supported controller hardware, you can set up many hard drives to act as one “logical” drive. In an operating system, these drives appear to it as one single drive.

It’s the job of the RAID controller to determine how your data gets stored and accessed. And it does this according to the way the “array” of hard drives got set up.

What is a RAID array?

OK, so we know that RAID is a term that gets used to describe how a bunch of hard drives get grouped together. When people talk about RAID arrays, that is what they mean. In a typical RAID array, you would have two or more physical hard drives connected to a RAID controller.

The controller is usually a PCI card (or similar) that slots into the computer’s motherboard. Each hard drive then gets connected to the controller using an ordinary SATA cable. When the RAID array first gets hooked up, the RAID “type” gets set up.

What are the different options for RAID arrays?

There are several different types of RAID arrays that you can set up. The most common ones are as follows:

  • RAID 0. This is also known as “striping.” With a RAID 0 configuration, two or more hard drives become one large logical drive. There is no redundancy with RAID 0, because if one hard drive fails the whole array gets wiped out. It’s a simple way of creating a large virtual storage pool, but is seldom used for storing crucial data;
  • RAID 1. This is also known as “disk mirroring.” Only two hard drives get used for RAID 1 arrays. That is because one hard drive mirrors the contents on the other. If one of the drives fails, the other can still get used until a replacement drive gets fitted. Once a new hard drive gets installed, the array can then get rebuilt and resume normal service;
  • RAID 5. This is also known as “striping with distributed parity.” It is akin to RAID 0 in that all the hard drives in the array form one large virtual drive. The only difference is that two drives get used to store data. Whereas the third gets used to store parity-checking data. RAID 5 arrays can often be slow due to the extra checks needed whenever data gets stored. You need at least three hard drives for RAID 5.

blakespot (obtained from Flickr)

There are also other RAID array types, although they don’t get used as often as the three examples above:

  • RAID 2. The same as RAID 5, except that data errors can get repaired. Other RAID arrays can only detect errors. RAID 2 needs at least then hard drives to operate;
  • RAID 3. The same as RAID 0, except that it needs a third hard drive to store parity-checking data;
  • RAID 4. The only difference between this and RAID 3 is the size of data used for parity checks;
  • RAID 6. This is an extension of RAID 5 and uses block-level parity checking. RAID 6 arrays need at least four hard drives.

As you can imagine, there are many different configurations available to you!

Are there any caveats to setting up a RAID array?

The one golden rule of setting up RAID arrays is that you should use the same make, model and size of hard drives. If you use different ones, data cannot get mirrored or striped across several hard drives. In fact, some controller hardware will refuse to work unless you remove different hard drives from the array first!

You should also use brand new hard drives when setting up a RAID array. It’s a well-known fact that hard drives only have a limited lifespan. This gets measured in hours and it’s known as MTBF or “mean time before failure.”

It’s likely that hard drives used in a RAID array will fail quicker than those in standard PCs due to the extra work they have to do. That is especially true if the systems they get used on run 24/7.

Do you need any special hardware to set up a RAID array?

By now you will know more about what RAID is and the basic steps to setting one up. But before you go offline and start compiling a shopping list to set up your own RAID array, be aware of the following:

  • You need a computer with plenty of space to store several hard drives;
  • Your motherboard must be new enough to support SATA;
  • Your computer’s power supply needs to be of a suitable wattage.