What You Need
The hard drives you use in the JBOD set can be of different sizes and from different manufacturers. If you’re working on a Mac Pro, you can use any available internal drive bays. Otherwise, you’ll need one or more external drive enclosures.
Erase the Drives Using the Zero Out Data Option
First, you’ll erase the hard drives within the JBOD RAID set. To reduce the risk of drive failures in the JBOD array, use one of the Disk Utility 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 increases the time it takes to erase the drives from a few minutes to an hour or more per drive.
Create the JBOD RAID Set
After the drives are erased, build the concatenated set.
Add Slices (Hard Drives) to Your JBOD RAID Set
It’s time to add members, or slices, to the set and create the finished RAID volume. 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 equals the combined total space of 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.
Extra: Tips for Using Your New JBOD RAID Set
As a concatenated disk set, your JBOD RAID array is not as susceptible to drive failure problems as a RAID 0 array. Nevertheless, you should still have an active backup plan in place if you need to rebuild your JBOD RAID set. Consider the use of backup software that runs on a predetermined schedule. It is possible to lose one or more disks in a JBOD RAID 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 might need to repair the drive and use a disk recovery application.
About JBOD RAID Sets
No matter what you call it—JBOD, concatenated, or spanning—this RAID type is about creating larger virtual disks. JBOD—the acronym for Just a Bunch Of Disks—is not a recognized RAID level, but Apple and most other vendors that created RAID-related products included JBOD support with their RAID tools. Among the many uses for JBOD RAID is expanding the effective size of a hard drive—just the thing if you have a file or folder that’s 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.
