What Is RAID?

No we’re not talking about killing insects.

We’re talking about a Redundant Array of Independent Disks.

And what does this have to do with web hosting? Well if you’ve been shopping for a dedicated server, you might have seen some web hosts offering RAID storage.

What Is RAID?

RAID as defined by its inventor stands for Redundant Array Of Inexpensive Disks. Later this has been changed to Redundant Array of Independent Disks by the computing industry.

Basically it’s a technology that allow the use of multiple hard drives to increase performance, reliability and capacity.

A RAID will use several disks and span data across all of them, making it look like a single hard drive to the operating system. Multiple drives grouped together is called an array.

Some arrays are redundant in a way that writes extra data from the original source on each hard drives. In case of failure, the defunct drive is taken offline and replaced without interruption. The new hard drive is then being rebuilt from the extra data previously written on the other drives from the array.

Other arrays are configured for faster access speed than a normal single drive.

All these different arrays arrangements are refered to as RAID Levels.

Let’s see the six standard RAID levels:

RAID 0

This is a stripped set without parity. This may increase performance and will surely increase storage space but it has no fault tolerance. If one disk fails, the array is destroyed and all data is lost.

If you have two (2) hard drives of 100GB each, you get a total of 200GB of storage.

RAID 1

This is a mirrored set without parity. In this case, the same data is always written to two drives at once so that one is a mirror from the other. If one this fails, the system keeps running as long as the other disk is working.

If you have two (2) hard drives of 100GB each, you get a total of 100GB of storage.

See InMotion Hosting Elite Plan for a RAID 1 dedicated server plan.

RAID 2

Level 2 uses bit-level striping with Hamming code ECC (error correcting code). It is implemented by splitting data at the bit level and spreading it over a number of data disks and a number of redundancy disks. This RAID level is less popular because of its cost and complexity.

RAID 3

Level 3 is a striped set with dedicated parity. The parity information is written to a dedicated parity disk. The failure of any disk in the array is tolerated.

If you have four (4) hard drives of 100GB each, you get a total of 300GB of storage as the fourth disk is dedicated to hold parity information.

RAID 4

Level 4 is identical to RAID 3 except it uses block level parity. It uses a dedicated parity disk but strips data into blocks (instead of bytes) across the array thus improving performance.

The total capacity is calculated the same way as RAID Level 3.

RAID 5

RAID Level 5 use a striped set with distributed parity. So unlike Levels 3 and 4 which uses a dedicated parity drive, RAID Level 5 distributes parity information across all drives in the array. To operate, all drives but one must be present.

The total capacity is calculated the same way as RAID Levels 3 and 4.

RAID 6

Level 6 uses block-level striping with dual distributed parity. It is the same thing as RAID 5 but provides fault tolerance from two drives failure. This especially used in high-availability and high capacity storage systems as rebuilding a replacement drive takes a lot of time.

The total capacity is calculated by [number of drives - 2] * [size of smallest drive].

So What Does This Mean To My Website?

Using RAID storage improves reliability and performance while preventing data loss. This doesn’t mean that you don’t need to have good backups but it prevents your web server from crashing in case of disk failure. You may get slower performance while the defunct hard drive is replaced but you have no downtime.

Of course, dedicated servers with RAID storage are more expensive. In the end, it all comes down to how much downtime you can afford.

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