Use Disk Utility to Create a RAID 0 (Striped) Array

Supercharge your Mac's performance

RAID 0, also known as a striped array, is one of the RAID levels supported by your Mac and OS X's Disk Utility. RAID 0 lets you assign two or more disks as a striped set. Once you create the striped set, your Mac sees it as a single disk drive, but when your Mac writes data to the RAID 0 striped set, the data is distributed across all the drives that make up the set.

Because each disk has less to do and writes to each disk occur concurrently, it takes less time to write the data. The same is true when reading data; instead of a single disk having to seek out and then send a large block of data, multiple disks each stream their part of the data stream. As a result, RAID 0 striped sets can provide a dynamic increase in disk performance, resulting in faster OS X performance on your Mac.

Information in this article applies to OS X Yosemite (10.10) through OS X Leopard (10.5).

RAID server in rack configuration
Matt Barnes Photography | Getty Images

Weighing the Benefits

Of course, with an upside (speed), there is almost always a downside. In this case, an increase in the potential for data loss caused by a drive failure. Since a RAID 0 striped set distributes data across multiple hard drives, the failure of a single drive in the RAID 0 striped set results in the loss of all data on the RAID 0 array.

Because of the potential for data loss with a RAID 0 striped set, it is highly recommended that you have an effective backup strategy in place before you create the RAID 0 array.

A RAID 0 striped set is all about increasing speed and performance. This type of RAID is a good choice for video editing, multimedia storage, and scratch space for applications, such as Photoshop, that benefit from faster drive access. It's also a good choice for speed demons out there who want to achieve high performance just because they can.

Disk Utility in OS X El Capitan dropped support for creating RAID arrays. If you use El Capitan, see the guide Use Terminal to Create and Manage a RAID 0 (Striped) Array in OS X.

In macOS Catalina (10.15) through macOS Sierra (10.12), DIsk Utility support for RAID returned, but the process differs from the one shown here. See how macOS Disk Utility creates RAID arrays.

What You Need to Create a RAID 0 Striped Set

The process of creating a RAID set is relatively simple and doesn't take much time. However, erasing all the drives in the RAID set — especially if you use the Zero Out Data option — can be a time-consuming process.

To create a RAID 0 striped array, you need a few essential components.

  • Disk Utility, which is included with OS X.
  • Two or more hard drives. The process of creating RAID 0 striped sets erases all the data on the hard drives. It's best if the hard drives you use are the same make and model, but this is not a requirement.
  • One or more drive enclosures. Mac Pro users may have internal drive bays available. Everyone else needs one or more external drive enclosures. If you are using multiple drive enclosures, they should have the same type of interface, such as FireWire, USB, Thunderbolt, or SATA.

Erase the Drives Using the Zero out Data Option

The hard drives you use as members of the RAID 0 striped set must first be erased.

A RAID 0 set can be severely affected by a drive failure, so take extra time and use one of Disk Utility's Security Options — Zero Out Data — when you erase each hard drive.

If your RAID set is made up of SSDs, do not use the Zero Out option. Instead, perform a standard erase.

When you zero out data, you force the hard drive to check for bad data blocks during the erasure process and mark any corrupt blocks as not to be used. This decreases the likelihood of losing data due to a failing block on the hard drive. It also significantly increases the amount of time it takes to erase the drives from a few minutes to an hour or more per drive.

Here's how to erase the drives:

  1. Connect the hard drives you intend to use to your Mac and powered them up.

  2. Launch Disk Utility, located at Applications > Utilities.

    The Disk Utility interface.
  3. Select one of the hard drives you are using in your RAID 0 striped set from the left pane of Disk Utility. Be sure to select the drive, not the volume name that appears indented under the drive's name.

    Selecting a hard drive.
  4. Click the Erase tab.

    Selecting Erase tab in Disk Utility.
  5. From the Volume Format drop-down menu, select Mac OS X Extended (Journaled).

    Choosing the format.
  6. Enter a name for the volume, such as StripeSlice1, for example.

    Naming the disk.
  7. Click the Security Options button.

    Selecting security options.
  8. Select the Zero Out Data security option and then click OK.

  9. Click the Erase button.

    Selecting Erase in Disk Utility.
  10. Repeat steps 3-9 for each additional drive you plan to use in the RAID 0 striped set. Give each drive a unique name.

Create the RAID 0 Striped Set

After you erase the drives you plan to use, you're ready to start building the striped set.

  1. Launch Disk Utility, located at Applications > Utilities, if the application is not already open.

    The disk utility program in macOS.
  2. Select one of the hard drives you are using in the RAID 0 striped set from the Drive/Volume list in the left pane of the Disk Utility window.

    Selecting a drive for the RAID stripe.
  3. Click the RAID tab.

    Selecting the RAID tab.
  4. Enter a name for the RAID 0 striped set. This is the name that will display on the desktop. This example uses the name VEdit, but any name will do.

    Naming the stripe array.
  5. Select Mac OS Extended (Journaled) from the Volume Format drop-down menu.

    Selecting the type of format.
  6. Select Striped RAID Set as the RAID type.

    Selecting the RAID type.
  7. Click the Options button.

    Selecting options in RAID setup.
  8. Set the RAID block size, which is influenced by the type of data you plan to store on the RAID 0 striped set. For general use, 32K is an acceptable block size. If you plan to store mostly large files, use a larger block size, such as 256K, to optimize the performance of the RAID.

  9. Make your choices on the options and click OK.

  10. Click the + (plus sign) button to add the RAID 0 striped set to the list of RAID arrays.

    Selecting the plus sign.

Add Slices to Your RAID 0 Striped Set

With the RAID 0 striped set now available in the list of RAID arrays, it's time to add drives — referred to as slices — to the set.

After you add all the hard drives to the RAID 0 striped set, you are ready to create the finished RAID volume for your Mac to use.

  1. Drag one of the hard drives from the left pane of Disk Utility onto the RAID array name you created — the one that will appear on the desktop.

    Selecting a slice.
  2. Drag each hard drive you want to add to the RAID 0 striped set to the RAID array name. A minimum of two slices, or hard drives, is required for a striped RAID. Adding more than two further increases performance.

    Slices added to the RAID set.
  3. Click the Create button.

    Selecting the create button.
  4. A "Creating RAID" warning sheet drops down, reminding you that all data on the drives that make up the RAID array will be erased. Click Create to continue.

During the creation of the RAID 0 striped set, Disk Utility renames the individual volumes that make up the RAID set to RAID Slice. It then creates the actual RAID 0 striped set and mounts it as a single hard drive volume on your Mac's desktop.

The total capacity of the RAID 0 striped set you create is equal to the combined total space offered by all members of the set, minus some overhead for the RAID boot files and data structure.

Close Disk Utility and use your RAID 0 striped set as if it were any other disk volume on your Mac.

Back up Your New RAID 0 Striped Set

Now that you have finished creating your RAID 0 striped set, here are a few tips about its use.

RAID successfully created using Disk Utility

Once again, the speed provided by a RAID 0 striped set does not come free. It is a trade-off between performance and data reliability. The loss of any single drive causes all data on the RAID 0 striped set to be lost.

To be prepared for a drive failure, you need a backup strategy that goes beyond the occasional backup. Consider the use of backup software that runs on a predetermined schedule. 

A RAID 0 striped set can significantly boost your system's performance, and it is a great way to increase the speed of video editing applications, specific applications such as Photoshop. Even games are faster if the games are i/o bound — they wait to read or write data from your hard drive.

After you create a RAID 0 striped set, you won't have any reason to complain about how slow your hard drives are.