How to configure a software RAID in macOS Sierra’s Disk Utility

Apple’s Disk Utility is usually the go-to app for reformatting, partitioning, and diagnosing storage devices on your Mac. For many years, the Disk Utility app stayed the same in terms of features and user interface. But that changed with OS X El Capitan; Disk Utility got a major facelift, and it also had its feature set modified. One of the major changes was that Apple removed any ability to set up and configure a redundant array of independent disks (RAID). You had to turn to a third-party app to do so.

In macOS Sierra’s Disk Utility (version 16.0, if you’re keeping track), the RAID features are back. Here’s how to set up and configure a software RAID using macOS Sierra’s Disk Utility. You can use Disk Utility if you, say, bought a multi-bay drive chassis and have filled it with spare hard drive mechanisms you had sitting in storage. Or you already have a RAID array and need to reconfigure it.

(In case you’re wondering, a software RAID is one where the Mac manages the RAID. A hardware RAID is a RAID array that includes a separate computer that manages the RAID. Learn more about hardware RAIDs. If you’re new to software RAIDs, here’s how to get started with the storage devices, then come back to this article to set up the RAID.)

How to set up a RAID in macOS Sierra’s Disk Utility

This will erase any data that exists on the disks you want to use for the RAID. Back up that data if you want to save it.

After you connect your storage devices to your Mac, launch Disk Utility. It’s located in the Utilities folder, which resides in your Applications folder. You can also press Shift-Command-U or select the Go > Utilities menu while in the Finder.
With Disk Utility open, you should see the main window. To get to the RAID tools, click on the File menu and select RAID Assistant.

How to access the RAID Assistant in macOS Sierra’s Disk Utility.
On the opening screen of the RAID Assistant, you select the RAID type. Which one should you choose?

(Striped) RAID 0: This one’s all about speed. It doesn’t offer data protection, so you’ll need to rely on another backup system, like Time Machine. But if backup isn’t an issue and you need the performance, go with RAID 0.
(Mirrored) RAID 1: The same data is written to all the drives. If a drive fails, your data is intact. When your Mac needs to read a file, the performance is faster because the data can be read by multiple drives.
Concatenated (JBOD): This simply takes your drives and uses them to create one storage volume. It doesn’t offer data protection or better speed.

macos sierra disk utility choose raid — Choosing a RAID format in macOS Sierra’s Disk Utility.

Choose your type, then click Next.

The next step is to select your storage devices. Disk Utility will show the drives eligible for the RAID format you select. The app shows the disk, and underneath each disk is a list of the partitions on that device. (When you take the space of a storage device and divide it during formatting, you are creating partitions.)
Click on the checkbox next to the disks you want to include in the RAID. When you select a disk, all the partitions are automatically selected.

Select the disks you want to include.
When setting up a RAID 1, you have to decide if a drive should be a RAID Slice or a Spare. A RAID Slice means the drive is an active part of the array and mirrors your data. A Spare is a drive that sits in waiting until a Slice fails, then data is mirrored to the spare automatically. If you have two drives, they each need to be set as RAID Slice. If you have more than two, you can set one as Spare.
Click the Next button after you’ve selected your disks.
Now you need to set the properties for your RAID.
- Name: Give your RAID a name, like you would your hard drive.
- Format: Most people should select Mac OS Extended (Journaled). Select Mac OS Extended (Case-Sensitive, Journaled) if you want files with the same name but with different case treatments (Science Report.txt and science report.txt, for example) to be saved as separate files.
- Type: This is what you selected back at the beginning of the procedure. To change it you have to start over.
- Capacity: This is based on the drives you selected in the previous step.
- Chunk size: Since data is written across drives, it is broken into pieces. Chuck size determines the size of those pieces. If you work with large files, like with video or 3D graphics, choose 128K or 256K. If you are a more general purpose user who does email, writes, or works in spreadsheets or databases, choose 32K or 64K.
- If you are building a RAID 1, you’ll see an option to “Automatically rebuild.” This means that if a drive is removed and then replaced, the data will automatically be restored to the new drive. Check this box if you want this option. If you don’t, you rebuild the RAID using the Disk Utility app.
RAID properties.
Once you click Next, your Mac will start to configure your RAID array, so don’t click it until you are ready.
Double-check your properties, then click Next. You’ll see a screen like the one below as your Mac goes to work configuring your RAID. This involves reformatting and partitions your disks and creating the RAID.