What are RAID Volumes and How to Set Them Up on Your Mac

 

Everyone has important data on their computers, and no matter which hard disk or SSD you use, there are chances of disk failure that results in data loss; that is exactly why we create backups. The thing with backups, though, is that you need to restore data from them, back into your computer. Why not use a fault-tolerant setup, instead? 

RAID is a combination of multiple disks that can be set up to be fault tolerant, in a sense. So that if one or more of the disks in the RAID volume fail, your data is still available to you.

In this article we’ll get you up to speed on what RAID actually is, and how you can use it to either keep data safely backed up, or to increase the read/write speed on the internal as well as external disks.

What is RAID?

RAID stands for Redundant Array of Independent Disks. Previously, it stood for Redundant Array of Inexpensive Disks, because it was originally meant to show that multiple inexpensive disks when RAIDed could perform equal (if not better) to high-end, large, enterprise storage disks.

RAID Levels

RAID has various types (or “levels” as they are called).  There are six of these, but Mac only allows for two (there’s a third option, but it’s not really a RAID setup). These are described below:

• RAID 1 : This level is called a “mirrored” RAID, and it does exactly what it sounds like. It mirrors the contents of one disk onto every single disk in the array. This means that if one or more of your disks fail, you can still recover all of the data as long as at least one disk in the array is functioning properly. This is possible because the data is copied on every disk in the array.

• RAID 0 : Also known as “striping” RAID, what this does is it combines multiple disks into one, larger volume. Data stored in such an array is almost equally distributed among all the disks in the array. This allows for faster reading and writing times. There is an issue however, if any one of the disks in your level 0 RAID fails, it becomes almost impossible to recover that data from the array because no disk has all of the data. This level is particularly useful for people who work with large files.

• CDS/JBOD: Concatenated Disk Set, also known as Just a Bunch Of Disks is not really a RAID setup. It simply allows you to concatenate a number of disks into one large logical volume. Say, for example, you had four 256 GB disks. CDS would allow you to concatenate them into one 1TB volume. This means that you will be able to save files onto these disks as if it was a single 1TB volume instead of four 256GB ones.

Now that we have given you a basic idea of what the various levels are, let’s dive headfirst into some RAID fun.

How To Setup RAID on Your Mac

Before Apple came out with OS X El Capitan, the process to set up RAID volumes was very simple. The graphical “Disk Utility” app on the Mac had a simple option to RAID a number of drives into either level 0,1 or to concatenate the drives (CDS/JBOD). When Apple redesigned the disk utility in OS X El Capitan, they quietly removed the RAID option. Why they did this is not what we are here to discuss. Instead, we are presenting the solution to your RAIDing problems in El Capitan.

Let’s dive into our trusted Terminal app. Turns out, the “diskutil” command has a “appleRAID” sub-command for creating RAIDs.

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