Raid 10 or Raid 1+0

In this section we will discuss raid 10 or raid 1+0 or striped mirrors or raid ten.

This is also a combination raid level, such as raid 01. In this level we first mirror two disks together and the the mirrors are striped.

This might sound a bit strange to do, but it actually makes a lot of sense.

This level is very common on hardware raid systems, but some vendors also makes this available on software raid. Veritas Volume Manager also makes use of raid 1+0. In Veritas, this level is known as a layered volume or volumes.

Layered, because the disks are first mirrored. These mirrors are then seen by the software as "disks". These, so called "disks", are then striped using the software. So, basically the mirrors are presented in a layer format to Veritas that uses them to stripe the disks with.

Below is a diagram of raid 1+0.

This level is also the most widely used of all levels. Well, software raid anyway. Hardware raid vendors have found other cool ways of using raid that makes cheaper and more redundant than raid 10.

With raid 1+0 you need the same resources as raid 01. The cool thing about raid 1+0 is that you can tolerate more than one disk failure before the volume is unusable. You can extend this redundancy by adding hot spares, just like raid 01.

Below is a diagram that shows this.

The thing here is, that the failed disks should not be part of the same mirror. If two disks failed with the purple mirror (diagram above), then we would loose the volume.

Let's say we used 10 disks in a raid 1+0 config, then we could theoretically loose up to 5 disks before the volume becomes unusable. Again, the disks that fail must not be the same disks in a mirror set.

Raid 10 gives the best performance and redundancy, but comes at a price. Like I said, You need twice the number of disks to create a raid 1+0 configuration.

If I can give you a tip here, spend the money on this level. You will not be disappointed. People try to use the cheaper raid 5 option and burn their fingers with performance. If you don't get the stripe size right with raid 5, you will get bad performance.

Bigger companies will go with raid 1+0. Not just that, they will also certainly use hardware raid instead of software raid.

It's a trade off. If you want performance, you'll have to spend some more. Just just how it is.

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