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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 (Just a Bunch Of Disks) is not actually a recognized RAID level, but Apple and most other vendors who create RAID-related products have chosen to include JBOD support with their RAID tools.
JBOD allows you to create a large virtual disk drive by concatenating two or more smaller drives together.
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.
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.
Published: 3/2/2009
Updated: 8/28/2015
JBOD RAID: What You Need
In order to create a JBOD RAID set, you will need a few basic components. One of the items you will need, Disk Utility, is supplied with OS X.
What You Need to Create a JBOD RAID Set
- OS X 10.5.x or later. The instructions given in this article use OS X Leopard. 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 JBOD RAID sets will erase all of the data on the hard drives. The hard drives you will 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 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 the guides here at About: Macs.
- 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.
Published: 3/2/2009
Updated: 8/28/2015
JBOD RAID: Erase the Drives
The hard drives you will be using as members of the JBOD RAID set must first be erased. And since we don’t want to have any drive failures in our JBOD array, 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.
Erase the Drives Using the Zero Out Data Option
- Make sure the hard drives you intend to use are connected to your Mac and powered up.
- Launch Disk Utility, located at /Applications/Utilities/.
- Select one of the hard drives you will be using in your JBOD RAID 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.
- Click the ‘Erase’ tab.
- From the Volume Format dropdown menu, select ‘Mac OS X Extended (Journaled)’ as the format to use.
- Enter a name for the volume; I’m using JBOD1 for this example.
- Click the ‘Security Options’ button.
- Select the ‘Zero Out Data’ security option, and then click OK.
- Click the ‘Erase’ button.
- Repeat steps 3-9 for each additional hard drive that will be part of the JBOD RAID set. Be sure to give each hard drive a unique name.
Published: 3/2/2009
Updated: 8/28/2015
JBOD RAID: Create the JBOD RAID Set
Now that we have erased the drives we will use for the JBOD RAID set, we’re ready to start building the concatenated set.
Create the JBOD RAID Set
- Launch Disk Utility, located at /Applications/Utilities/, if the application is not already open.
- Select one of the hard drives you will be using in the JBOD RAID set from the Drive/Volume list in the left pane of the Disk Utility window.
- Click the ‘RAID’ tab.
- Enter a name for the JBOD RAID set. This is the name that will display on the desktop. Since I will be using my JBOD RAID set for storing a large set of databases, I’m calling mine DBSet, but any name will do.
- Select ‘Mac OS Extended (Journaled)’ from the Volume Format dropdown menu.
- Select ‘Concatenated Disk Set’ as the RAID type.
- Click the ‘Options’ button.
- Click the ‘+’ (plus) button to add the JBOD RAID set to the list of RAID arrays.
Published: 3/2/2009
Updated: 8/28/2015
With the JBOD RAID set now available in the list of RAID arrays, it’s time to add members or slices to the set.
Add Slices to Your JBOD RAID Set
Once you add all of the hard drives to the JBOD RAID set, you are ready to create the finished RAID volume for your Mac to use.
- 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.
- Repeat the above step for each hard drive you wish to add to your JBOD RAID set. A minimum of two slices, or hard drives, is required for a JBOD RAID. Adding more than two will further increase the size of the resulting JBOD RAID.
- Click the ‘Create’ button.
- 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 JBOD RAID set, Disk Utility will rename the individual volumes that make up the RAID set to RAID Slice; it will then create the actual JBOD RAID set and mount it as a normal hard drive volume on your Mac’s desktop.
The total capacity of the JBOD RAID 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 JBOD RAID set as if it were any other disk volume on your Mac.
Published: 3/2/2009
Updated: 8/28/2015
Now that you have finished creating 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. (I have sometimes been able to simply mount a volume and gain access to the data without problems, but I wouldn’t count on it.) You will probably need to repair the drive and maybe even use a disk recovery application.
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.”
Consider the use of backup software that runs on a predetermined schedule. Take a look at: Mac Backup Software, Hardware, and Guides for Your Mac
The above warning doesn’t mean that a JBOD RAID set is a bad idea. It’s a great way to effectively increase the size of the hard drive your Mac sees.
It’s also a great way to recycle smaller drives you may have laying around from older Macs, or reuse the leftover drives from a recent upgrade.
No matter how you slice it, a JBOD RAID set is an inexpensive way to increase the size of a virtual hard drive on your Mac
Published: 3/2/2009
Updated: 8/28/2015
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