Disk Utility Can Create a JBOD RAID Set for Your Mac

Use several drives to create a single large volume

A JBOD RAID set or array, also known as a concatenated or spanning RAID, is one of the many RAID levels supported by OS X and Disk Utility

JBOD—the acronym for Just a Bunch Of Disks—is not actually a recognized RAID level, but Apple and most other vendors that create RAID-related products have chosen to include JBOD support with their RAID tools.

JBOD supports a large virtual disk drive by concatenating two or more smaller drives. The individual hard drives that make up a JBOD RAID can be of different sizes and manufacturers. The total size of the JBOD RAID is the combined total of all the individual drives in the set.

These instructions apply to macOS Yosemite or earlier. El Capitan and newer versions of macOS removed RAID capability from Disk Utility.

What Does a JBOD RAID Array Do?

There are many uses for JBOD RAID, but it’s most often used to expand the effective size of a hard drive—just the thing if you find yourself with a file or folder that is getting too large for the current drive. You can also use JBOD to combine smaller drives to serve as a slice for a RAID 1 (Mirror) set.

No matter what you call it—JBOD, concatenated or spanning—this RAID type is all about creating larger virtual disks.

OS X and macOS both support creating JBOD arrays.

If you're using OS X El Capitan, you're out of luck if you want to use Disk Utility to create or manage any RAID array including JBOD. When Apple released El Capitan, it removed all RAID functions from Disk Utility. You can still use RAID arrays, although you have to use Terminal or an app such as SoftRAID Lite.

What You Need

To create a JBOD RAID set, you need a few basic components. One of the items you need, Disk Utility, is supplied with OS X.

What You Need to Create a JBOD RAID Set

  • OS X 10.5.x or later
  • Disk Utility
  • Two or more hard drives. The process of creating JBOD RAID sets erases all the data on the hard drives. The hard drives you use in the JBOD set can be of different sizes and from different manufacturers.
  • One or more drive enclosures. Mac Pro users may have internal drive bays available. Everyone else needs one or more external drive enclosures.

Erase the Drives

The hard drives within the JBOD RAID set must first be erased. To reduce the risk of drive failures in the JBOD array, use one of Disk Utility’s security options, Zero Out Data, when each drive erases.

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 step 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.

How to Erase the Drives Using the Zero Out Data Option

  1. Launch Disk Utility and select one of the hard drives for the JBOD RAID set from the list in the sidebar. Select the drive, not the volume name that appears indented under the drive’s name. Then, click the Erase tab.

    Disk Utility on Mac with drive selected and Erase tab highlighted
  2. From the Volume Format drop-down menu, select Mac OS X Extended (Journaled) as the format to use.

    Disk Utility with Mac OS Extended (Journaled) selected as Format
  3. Enter a name for the volume in the Name field.

    Disk Utility with drive name highlighted
  4. Click the Security Options button. Select the Zero Out Data security option and then click OK.

    Disk Utility with Security Options highlighted
  5. Click the Erase button.

    Disk Utility with Erase selected
  6. Repeat this process for each additional hard drive that will be part of the JBOD RAID set. Give each hard drive a unique name.

Create the JBOD RAID Set

After the drives are erased, build the concatenated set.

  1. In Disk Utility, select one of the hard drives from the drive/volume list in the left sidebar. Then click the RAID tab.

    Untitled disk selected in Disk Utility sidebar and RAID highlighted
  2. Enter a name in the field next to RAID Set Name for the JBOD RAID set that displays on the desktop.

    Disk Utility with RAID Set Name highlighted
  3. Select Mac OS Extended (Journaled) from the Format drop-down menu.

    Mac OS Extended (Journaled) selected in disk Format menu
  4. Select Concatenated Disk Set in the RAID Type field.

    Concatenated Disk Set selected a RAID type in Disk Utility

Add Slices (Hard Drives) to Your JBOD RAID Set

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

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

  1. Drag one of the hard drives for the array from the left sidebar of Disk Utility onto the RAID array name you created in the previous step.

    A hard drive selected for a new RAID array
  2. Drag the remaining hard drives intended for the JBOD RAID set onto the RAID array name. A minimum of two slices, or hard drives, is required for a JBOD RAID. Adding more than two further increases the size of the resulting JBOD RAID.

  3. Click the Create button. A Creating RAID warning sheet drop downs, reminding you that all data on the drives that make up the RAID array will be erased.

    Create button highlighted in Disk Utility RAID tab
  4. Click Create to continue.

During the creation of the JBOD RAID set, Disk Utility renames the individual volumes that make up the RAID set to RAID Slice; it then creates the actual JBOD RAID set and mounts it as a normal hard drive volume on your Mac’s desktop.

The total capacity of the JBOD RAID 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.

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

Tips for Using Your New JBOD RAID Set

Now that you created your JBOD RAID set, here are a few tips about its use.

Backups

Although a concatenated disk set—your JBOD RAID array is not as susceptible to drive failure problems as a RAID 0 array—you should still have an active backup plan in place should you ever need to rebuild your JBOD RAID set.

Drive Failure

It is possible to lose one or more disks in a JBOD RAID due to hard drive failure, and still have access to the remaining data. That’s because data stored on a JBOD RAID set remains physically on individual disks. Files do not span volumes, so data on any remaining drives should be recoverable. That does not mean that recovering data is as simple as mounting a member of the JBOD RAID set and accessing it with the Mac’s Finder. You will probably need to repair the drive and maybe even use a disk recovery application.

Consider the use of backup software that runs on a predetermined schedule.