RAID management in OS X has existed throughout multiple iterations of the popular Mac OS. Up until El Capitan, RAID volume creation was as simple as selecting the tab in Disk Utility and a few clicks later, your RAID or concatenated volume would be ready.
El Capitan's redesign of Disk Utility changed everything, including the removal of RAID volume management through the GUI. However, RAID support is still alive and well in Terminal. Let me show you how it's done.
Building a RAID array
1. Launch Terminal and execute the following command to obtain the disk IDs since we will need those to complete the build process (Figure A).
2. Making a note of the disk IDs for which disks will be part of the array, next run you'll need to decide which type of RAID array to build: Striped (Storage) or Mirrored (Backup). A striped array (RAID 0) is developed for performance since it combines two or more disks into one virtual one and the data is written across the drives simultaneously, speeding up the read/write times. RAID 0 offers no fault tolerance, so when one disk dies the data is lost — be sure to keep backups aplenty. To select RAID 0 (Storage), execute the command below (Figure B).
diskutil appleRAID create stripe Storage JHFS+ diskID1 diskID2
By contrast, a mirrored array (RAID 1) features fault tolerance by design. Data is written to both drives at the same time so each drive has a valid copy of the data stored. If one drive dies, the remaining drive will continue to function without loss of data. RAID1 does slow down performance at the cost of the redundancy. To select RAID 1 (Backup), execute the command below (Figure C).
diskutil appleRAID create mirror Backup JHFS+ diskID1 diskID2
3. The process takes minutes to complete. Once it's done, rerun the command from step 1 to verify the newly created RAID volume (Figure D).
Destroying a RAID array
1. Identify the RAID volume's disk ID and make a note of it.
2. Execute the following command from Terminal to delete the RAID array and split the disks back to their previous standalone format (Figure E).
diskutil appleRAID delete diskID
Note: Breaking the RAID array can and most likely will render the data on the disk useless and unrecoverable. Make certain the data is no longer needed or backed up before proceeding.
What's your experience with RAID?
Do you have any horror stories or difficulties utilizing the technology? We want to hear from you in the comments.
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Jesus Vigo is a Network Administrator by day and owner of Mac|Jesus, LLC, specializing in Mac and Windows integration and providing solutions to small- and medium-size businesses. He brings 19 years of experience and multiple certifications from several vendors, including Apple and CompTIA.