Hack Old USB Drives into a Mini RAID on a Mac

Most of us have a lot of old USB thumb drives lying around. Sometimes you just got a new larger capacity or less grubby looking one, but often you just accumulate them as they are the most popular storage medium and are used and discarded as needed because they are cheap.

Once they have served their purpose, the ones you don’t use just sit in a drawer or on a desk until you throw them away or lose them (and you don’t even remember it existed). But what if you could combine them and make a higher capacity drive to plug into a media player in a TV or back up your USB drives that are in use?

This article explains how to turn old USB drives into a mini RAID to give them new life.

RAID stands for Redundant Array of Independent Disks. A RAID combines multiple drives into a single “logical unit” for the purposes of what is called data redundancy or performance improvement, so in other words, either secure, fast, big, or combos of all three.

Data is spread across the drives in one of several “RAID levels” depending on the intended use. Each RAID level contains different levels of error correction, distribution of data etc. but we don’t need to know all that – the three modes we will concern ourselves with here are “striped”, “mirrored” and “JBOD”.


“Striped” combines drives of equal size as a large fast unit. “Mirrored” takes one drive and copies it to all the others continuously so it is secure; the data never gets lost because it’s backed up multiple times automatically. If one drive fails, it can be replaced. JBOD (meaning “Just A Bunch Of Disks”) chains together drives of any size and makes them a continuous logical drive.

Obviously the mode you choose depends on the use. Striped is faster, Mirrored is the best backup but JBOD uses every drive you have and makes a big drive.

To make a collection of USB drives into a RAID on OS X is simple. First plug all the USB drives you have into a USB hub. (See above) They will all show up on the desktop.

separate disks 2

Open Disk Utility either by going to “Applications -> Utilities -> Disk Utility” or from the Finder, press “Command + Shift + U” to go to the Utilities folder and start Disk Utility.

All the drives you have attached show up in the panel.

discs mounted

Select one of the drives you want to turn into a RAID and click the RAID tab.

click raid tab

You will be presented with a range of options: naming the RAID and which type of RAID you want to make, either mirrored, striped or concatenated (JBOD). In this case, we will select concatenated as the drives are of assorted 4Gb, 8Gb and 16Gb sizes. If they were all the same, you can use striped or mirrored. 

Note: you CAN use drives of different sizes in the other two modes but the drives will be partitioned to be the same size as the smallest drive.

choose raid level

Drag every drive you want to be a part of the RAID. Warning: Do this carefully as these drives will be formatted and you DON’T want to include your system drive by accident.

You will see the projected final size of the finished drive in the panel above the drive window.

disks dragged in

Press the “Create” button and you will be warned that you are about the delete all these disks and make them into a RAID.

are you sure you want to

Click OK and the drives will all be unmounted, partitioned and formatted one by one.

partition map

When it’s finished and the drive has “spun up” . . .

waiting to spin up

. . . the new drive virtual unit will be displayed on the desktop ready for use.

raid slices made 2

If you have a bunch of old USB drives, this is a good way to make good use of them rather than throwing them away. One thing to note is that old USB drives, especially USB 1.0, are slow, so it will take a while to copy stuff to them, but hey, you have a free SSD drive of much higher capacity than the component parts, so speed is a luxury. Obviously faster USB 3.0 drives will be better if have them.