How to manage RAID volumes in El Capitan

If Apple's elimination of RAID volumes from the retooled Disk Utility has got you down, fret not. Learn the commands necessary to build and destroy RAID volumes in El Capitan.

Image: Jesus Vigo/TechRepublic

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.

SEE: OS X El Capitan: The smart person's guide

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).

diskutil list

Figure A

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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

Figure B

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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

Figure C

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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).

Figure D

Image: Jesus Vigo/TechRepublic

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

Figure E

Image: Jesus Vigo/TechRepublic

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 seve...

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