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

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RAID 0 Striped: What Is a RAID 0 Striped Array?

RAID server in rack configuration
RAID arrays can be housed in specially designed external enclosures. But it is not a requirement for general purpose RAID systems. Matt Barnes Photography | Getty Images

RAID 0, also know as a striped array, is one of the many 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 will see it as a single disk drive. But when your Mac writes data to the RAID 0 striped set, the data will be distributed across all of the drives that make up the set. Because each disk has less to do and writes to each disk are done 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.

Of course with an up side (speed), there is almost always a ​down side; 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 will result 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 can be 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.

If your using macOS Sierra or later, you can still use Disk Utility to create and manage RAID arrays, but the process is a bit different. You can find out more in the guide:

02
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RAID 0 Striped: What You Need

Disk Utilities RAID funcations
Creating a RAID array starts by selecting the type of RAID to create. Screen shot courtesy of Coyote Moon, Inc.

In order to create a RAID 0 striped array, you will need a few basic components. One of the items you will need, Disk Utility, is supplied with OS X.

Note: The version of Disk Utility included with OS X El Capitan dropped support for creating RAID arrays. Fortunately later versions of the macOS do includ RAID support. If you're using El Capitan, you can use the guide: ​

What You Need to Create a RAID 0 Striped Set

  • OS X 10.5.x or later. The instructions given in this article were tested on OS X Leopard through OS X Yosemite. While these instructions should work for both past and future versions of OS X, some of the steps, nomenclature, or images shown in this article may be different.
  • Disk Utility. This is included with OS X.
  • Two or more hard drives. Be aware that the process of creating RAID 0 striped sets will erase all of 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 will need one or more external drive enclosures. If you are using multiple drive enclosures, they should ideally be the same make and model, or at least have the same type of interface, (i.e., FireWire, USB, Thunderbolt, or SATA). This article will not provide instructions for installing and using external enclosures; instead, we will assume you already have them available, or will be building them using one of our guides.
  • A few hours of your time. The process of creating a RAID set is fairly simple and doesn't take much time, but we will be erasing all of the drives in the RAID set using the Zero Out data option. This somewhat time-consuming process ensures maximum reliability.

    Warning: If your RAID set is made up of SSDs, do not use the zero out option. Instead just perform a standard erase.

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RAID 0 Striped: Erase Drives

Disk Utility erasing a drive.
Each disk that will become a member of a RAID array must be erased and formatted correctly. Screen shot courtesy of Coyote Moon, Inc.

The hard drives you will be using as members of the RAID 0 striped set must first be erased. And since a RAID 0 set can be severely impacted by a drive failure, we're going to take a little extra time and use one of Disk Utility's security options, Zero Out Data, when we erase each hard drive.

When you zero out data, you force the hard drive to check for bad data blocks during the erasure process and mark any bad 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.

If your using solid state drives for your RAID, you should not use the zero out option as this can cause premature ware and reduce the lifetime of an SSD.

Erase the Drives Using the Zero Out Data Option

  1. Make sure the hard drives you intend to use are connected to your Mac and powered up.
  2. Launch Disk Utility, located at /Applications/Utilities/.
  3. Select one of the hard drives you will be using in your RAID 0 striped set from the list on the left. Be sure to select the drive, not the volume name that appears indented under the drive's name.
  4. Click the 'Erase' tab.
  5. From the Volume Format drop-down menu, select 'Mac OS X Extended (Journaled)' as the format to use.
  6. Enter a name for the volume; I'm using StripeSlice1 for this example.
  7. Click the 'Security Options' button.
  8. Select the 'Zero Out Data' security option, and then click OK.
  9. Click the 'Erase' button.
  10. Repeat steps 3-9 for each additional hard drive that will be part of the RAID 0 striped set. Be sure to give each hard drive a unique name.
04
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RAID 0 Striped: Create the RAID 0 Striped Set

Disk Utility RAID creation
Be sure and create the RAID 0 array before trying to add any disks. Screen shot courtesy of Coyote Moon, Inc.

Now that we have erased the drives we will use for the RAID 0 striped set, we're ready to start building the striped set.

Create the RAID 0 Striped Set

  1. Launch Disk Utility, located at /Applications/Utilities/, if the application is not already open.
  2. Select one of the hard drives you will be using in the RAID 0 striped set from the Drive/Volume list in the left pane of the Disk Utility window.
  3. Click the 'RAID' tab.
  4. Enter a name for the RAID 0 striped set. This is the name that will display on the desktop. Since I will be using my RAID 0 striped set for video editing, I'm calling mine VEdit, but any name will do.
  5. Select 'Mac OS Extended (Journaled)' from the Volume Format drop-down menu.
  6. Select 'Striped RAID Set' as the RAID type.
  7. Click the 'Options' button.
  8. Set the RAID Block Size. The block size is dependent on the type of data you will be storing on the RAID 0 striped set. For general use, I suggest 32K as the block size. If you will be storing mostly large files, consider 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) button to add the RAID 0 striped set to the list of RAID arrays.
05
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RAID 0 Striped: Add Slices (Hard Drives) to Your RAID 0 Striped Set

Disk Utility being used to add slices to a RAID array.
After the RAID array is created you can add slices or members to the RAID set. Screen shot courtesy of Coyote Moon, Inc.

With the RAID 0 striped set now available in the list of RAID arrays, it's time to add members or slices to the set.

Add Slices to Your RAID 0 Striped Set

Once you add all of 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-hand pane of Disk Utility onto the RAID array name you created in the last step.
  2. Repeat the above step for each hard drive you wish to add to your RAID 0 striped set. A minimum of two slices, or hard drives, is required for a striped RAID. Adding more than two will further increase performance.
  3. Click the 'Create' button.
  4. A 'Creating RAID' warning sheet will drop 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 will rename the individual volumes that make up the RAID set to RAID Slice; it will then create the actual RAID 0 striped set and mount it as a normal hard drive volume on your Mac's desktop.

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

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

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RAID 0 Striped: Using Your New RAID 0 Striped Set

RAID successfully created using Disk Utility
Once the RAID set is created, Disk Utility will register the array and bring it online. Screen shot courtesy of Coyote Moon, Inc.

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

Backup

I can't say this strongly enough: The speed provided by a RAID 0 striped set does not come free. It is a tradeoff between performance and data reliability. In this case, we have skewed the equation towards the performance end of the spectrum. The result is that we can be adversely affected by the combined failure rate of all of the drives in the set. Remember, any single drive failure will cause all data on the RAID 0 striped set to be lost.

In order to be prepared for a drive failure, we need to ensure that we not only have backed up the data, but that we also have a backup strategy that goes beyond the casual, "Hey, I'll back up my files tonight because I happened to think of it."

Instead, consider the use of backup software that runs on a predetermined schedule. You can take a look at:

Mac Backup Software, Hardware, and Guides for Your Mac

The above warning doesn't mean that a RAID 0 striped set is a bad idea. It can significantly boost your system's performance, and it can be a great way to increase the speed of video editing applications, specific applications like Photoshop, and even games, if the games are i/o bound, that is, they wait to read or write data from your hard drive.

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