How to Set Up RAID in macOS Sierra

While the feature was removed in El Capitan, native software RAID has returned in macOS Sierra. You can access it through Disk Utility, and the graphical interface makes it easy to configure either RAID 1 or RAID 0.

Which RAID?

As you probably know, RAID stands for Redundant Array of Independent Disks. It’s a protocol that allows users to combine multiple physical disks into a single logical data storage structure. While many different schemes exist, macOS provides native software support for RAID 1 and RAID 0.

RAID 1, commonly called “mirroring,” involves two or more hard drives with exactly the same data. This isn’t backup – any user errors or corruptions will immediately propagate to both drives. However, RAID 1 does provide protection against physical drive failure.

RAID 0, commonly called “striping,” shares data across both disks without duplication. This can lead to a significant boost in performance, since both disks can work together to provide data. RAID 0 includes no duplication, and if one drive fails in a RAID 0 array, the whole thing is hosed. This is awesome for applications that require high disk performance but can tolerate a lower level of data integrity, like scientific computing or AV processing.

macOS also offers JBOD, which stands for “Just A Bunch Of Disks.” It’s as prosaic as it sounds. The OS combines two or more drives under one drive name and icon, creating one “logical” disk out of multiple physical disks. You won’t get any of the features or benefits of RAID 0 or 1. JBOD is very much like a directory containing multiple physical disks and nothing more.

Setting Up RAID in Disk Utility

1. Open Disk Utility. You can find it under “/Applications/Utilities” or by typing “Disk Utility” into Spotlight.

2. Click the File menu and choose the menu option labeled “RAID Assistant…”

3. In the next dialog box choose the type of RAID array you’d like to create. Click Next when you’re ready.

4. Click the tick boxes next to the drives you want to include in your new RAID array. Regardless of the kind of array you chose in the last step, this will be the same screen.

5. Give your RAID array a clever name. Everything else can stay on the default settings. Click Next when you’re done.

6. Confirm that you’ve selected the right disks, and click “Create” to finalize the array. Note that this will automatically format the disks and destroy any data on the drives.

7. Wait for your array to spin up. This might take a couple minutes, depending on the size of your array and your interface speed.

8. Applaud! You’re done.

9. If you return to the main Disk Utility window, you’ll see your brand new RAID array in the sidebar. Click on it to see more info about the array.

If you have selected RAID 0, the disks you selected will be automatically striped together. If you’ve selected RAID 1, those disks will become mirrors of one another. And if you’ve selected JBOD, all those disks will now appear under a single name and icon within the operating system, but no other changes will take place.

Deleting a RAID Array

If you need to delete a RAID array, that’s also possible. Don’t forget that if you’re splitting up a RAID 0 array, all your data will be destroyed. And not destroyed in the normal “still recoverable” way – destroyed in the “irrevocably gone” way.

1. Open Disk Utility.

2. Select your RAID array in the sidebar.

3. Click the button labeled “Delete RAID…”

4. Confirm your choice in the next dialog box. Be absolutely certain that you intend to completely erase all information on the disks.

5. Wait while the array erases itself.

6. When you’re done, the array will be gone from the sidebar.

7. You will need to manually reformat the array’s constituent drives before you can reuse them. Select one of the former array’s disks and click the Erase button in the toolbar. If this button is greyed out, make sure you’ve selected the volume in the sidebar that starts with “RAID Member” rather than the disk itself.

7. Select a disk format in the next dialog box. Typically, this would be automatically filled in, but here you’ll need to make an affirmative selection. Mac OS Extended (Journaled) is ideal. Click Erase.

Conclusion

RAID o or RAID 1 can both be configured easily through macOS Sierra’s Disk Utility app. If you want performance and can tolerate low data integrity, go for RAID 0. If you want to protect against disk failure, check out RAID 1. And if you just want to combine a bunch of disks under a single icon, JBOD is for you.