Apple didn’t only return RAID support to Disk Utility; it changed the user interface enough to ensure that your previous method of working with RAID arrays would require learning a few new tricks.
RAID 0, 1, 10, and JBOD
Disk Utility can be used to create and manage the same four RAID versions it has always been capable of working with:
RAID 0 (Striped) RAID 1 (Mirrored) RAID 10 (Mirrored set of Striped drives) JBOD (Just a Bunch Of Disks)
There are other RAID types and third-party RAID apps that can manage RAID arrays for you. In some cases, they do a better job.
Why Use RAID?
RAID arrays can solve some problems you may experience with your Mac’s current storage system. Perhaps you want faster performance, such as is available from various SSD offerings, until you realized a large SSD is outside your budget. RAID 0 can be used to boost performance at a reasonable cost. Similarly, you can use RAID 1 to increase the reliability of a storage array when your needs demand high reliability. You can even combine RAID modes to produce a storage array that’s fast and reliable.
Back Up First
The process of creating a RAID array in Disk Utility involves erasing the disks that make up the array. If you have data on these disks that you want to keep, back up the data before proceeding. If you need assistance with creating a backup, check out Mac Backup Software, Hardware, and Guides for Your Mac.
Create and Manage a Striped RAID 0 Array
Use Disk Utility to create and manage a Striped (RAID 0) array, which splits data between two or more disks to provide faster access for data reads from and data writes to the disks.
RAID 0 Requirements
Disk Utility requires a minimum of two disks to create a striped RAID 0 array. While there’s no requirement for the disks to be the same size or from the same manufacturer, disks in a striped array should match to ensure the best performance and reliability.
RAID 0 Array Failure Rate
Additional disks beyond the minimum can be used to increase overall performance, although it comes at the cost of increasing the overall failure rate of the array. The method to calculate the failure rate of a striped array, assuming all disks in the array are the same, is as follows: 1 - (1 - the published failure rate of a single disk) raised to the number of slices in the array Slice is the term commonly used to refer to a single disk within a RAID array. The speedier you want to go, the greater the risk of failure. You should have a backup plan in place if you’re creating a striped RAID array.
Use Disk Utility to Create a RAID 0 Array
For this example, assume you’re using two disks to create a fast striped RAID 0 array. Disk Utility creates your new RAID array. Once the process is complete, the RAID Assistant displays a message that the process was successful, and your new striped array is mounted on your Mac’s desktop. For example, if the RAID array is being used to speed up the macOS operating system, a chunk size of 64K would work well since most system files are generally small in size. If you plan to use the striped array to host your video or multimedia projects, the largest available chunk size may be a better choice.
Delete a RAID 0 Array
When you no longer need the striped RAID 0 array you created, Disk Utility can remove it, breaking it back down to the individual disks, which you can then use as you see fit.
Create and Manage a RAID 1 Array
RAID Assistant, a component of Disk Utility in macOS, supports multiple RAID arrays. This section looks at creating and managing a RAID 1 array, also known as a mirrored array. Mirrored arrays replicate data across two or more disks, with the primary goal of increasing reliability by creating data redundancy, assuring that if a disk in a mirrored array were to fail, data availability would continue without interruption.
RAID 1 Array Requirements
RAID 1 requires a minimum of two disks to make up the RAID array. Adding more disks to the array increases overall reliability by the power of the number of disks in the array. You can learn more about RAID 1 requirements and how to calculate reliability at RAID 1: Mirroring Hard Drives.
Use Disk Utility to Create a RAID 1 Array
Make sure the disks that will make up your RAID 1 mirrored array are attached to your Mac and mounted on the desktop.
Add Slices to a Mirrored RAID 1 Array
There may come a time when you want to add slices to the mirrored RAID 1 array. You may want to do this to increase reliability or to replace older slices that are showing issues.
Remove a RAID 1 Slice
You can remove a RAID slice from a RAID 1 mirror provided there are more than two slices. You may want to remove a slice to replace it with another newer disk or use it as part of a backup or archiving system. Disks that are removed from a RAID 1 mirror usually have the data preserved. This allows you to archive the data in a safe location without disturbing the RAID array.
Repair a RAID 1 Array
It may seem like the Repair function should be similar to Disk Utility’s First Aid, except geared to the needs of a RAID 1 mirrored array. However, Repair has an entirely different meaning here. Essentially, Repair is used to add a new disk to the RAID set and force a rebuild of the RAID set to copy the data to the new RAID member. Once the “repair” process is complete, remove the RAID slice that failed and prompted you to run the Repair process. Repair is the same as using the add (+) button and selecting New Member as the type of disk or volume to add. Since you have to manually remove the bad RAID slice using the minus (-) button when using the Repair feature, you can use Add (+) and Remove (-) instead.
Remove a Mirrored RAID 1 Array
You can completely remove a mirrored array, returning each slice that makes up the array to general use by your Mac.
Create and Manage RAID 10 or RAID 01
The RAID Assistant that’s included with Disk Utility and macOS supports creating compound RAID arrays—that is, arrays that involve the combining of striped and mirrored RAID sets. The most common compound RAID array is a RAID 10 or RAID 01 array. RAID 10 is the striping (RAID 0) of a pair of RAID 1 mirror sets (a striping of mirrors), while RAID 01 is the mirroring of a pair of RAID 0 striped sets (a mirroring of stripes). This example creates a RAID 10 set using Disk Utility and the RAID Assistant. You can use the same concept for making a RAID 01 array, though RAID 10 is more common. RAID 10 is often used when you want to have the speed of a striped array but don’t want to be vulnerable to the failure of a single disk, which, in a normal striped array, would cause you to lose all your data. By striping a pair of mirrored arrays, you increase reliability while maintaining the improved performance in a striped array. The reliability improvement comes at the cost of doubling the number of disks needed.
RAID 10 Requirements
RAID 10 requires at least four disks, broken into two striped sets of two disks. The disks should be from the same manufacturer and be of the same size, although technically, it’s not a requirement.
Use Disk Utility to Create a RAID 10 Array
To create a RAID 10 array:
Create and Manage a JBOD Array
The final RAID set Disk Utility can make is commonly referred to as JBOD (Just a Bunch of Disks)—a concatenation of disks. Technically, it isn’t a recognized RAID level, as RAID 0 and RAID 1 are. Nevertheless, it’s a useful method of using multiple disks to create a single larger volume for storage.
JBOD Requirements
The requirements for creating a JBOD array are loose. Disks that make up the array can be from multiple manufacturers, and disk performance doesn’t need to be matched. JBOD arrays provide neither a performance increase nor a reliability increase. Although it may be possible to recover data using data recovery tools, a single disk failure will likely lead to lost data. As with all RAID arrays, having a backup plan is a good idea.
Use Disk Utility to Create a JBOD Array
Before you begin, make sure the disks you want to use for the JBOD array are attached to your Mac and mounted on the desktop.
Add Disks to a JBOD Array
If you run out of space on your JBOD array, you can increase its size by adding disks to the array.
Remove a Disk From a JBOD Array
It’s possible to remove a disk from a JBOD array, although it has issues. The disk being removed must be the first disk in the array, and there must be enough free space on the remaining disks to move the data from the disk you’re planning to remove to the disks that remain in the array. Resizing the array in this manner requires that the partition map be recreated. Any failure in any part of the process causes the process to abort and the data in the array to be lost.
Delete a JBOD Array
You can delete a JBOD array, returning each disk that makes up the JBOD array to general use.
