software raids


macOS Sierra (10.12) saw the return of RAID support to the Apple Disk Utility, a feature that was removed with OS X El Capitan (10.11). With the return of RAID support in Disk Utility, you no longer need to resort to using Terminal to create and administer your RAID systems.

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.

Information in this article applies to macOS Big Sur (11) through macOS Sierra (10.12).

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:

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.

  1. Launch Disk Utility, located at /Applications/Utilities/.

  2. Make sure the two disks you wish to use in the RAID array are present in the Disk Utility sidebar. They don’t need to be selected at this point; just make sure they are successfully mounted on your Mac.

  3. Select RAID Assistant from the Disk Utility File menu.

  4. In the RAID Assistant window, select Striped (RAID 0) and then select Next.

    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.

    1. Launch Disk Utility, located at /Applications/Utilities/.

    2. From the Disk Utility File menu, select RAID Assistant.

    3. In the RAID Assistant window, select Concatenated (JBOD) and then select Next.

    4. In the Disk selection list that appears, pick two or more disks that you want to use in the JBOD array. You can select an entire disk or a volume on a disk.

    5. Make your selections and select Next.

    6. Enter a name for the JBOD array, a format to use, and a Chunk size. Be aware that chunk size has little meaning in a JBOD array. Still, you can follow Apple’s guidelines of selecting a larger chunk size for multimedia files and a smaller chunk size for databases and operating systems.

    7. Make your selections and then select Next.

    8. You are warned that creating the JBOD array erases all data currently stored on the disks that make up the array. Select Create.

    9. The RAID Assistant creates the new JBOD array. Once it is complete, select Done.

    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.

    Make sure the disks you plan to add to the existing JBOD array are attached to your Mac and mounted on the desktop.

    1. Launch Disk Utility if it isn’t open.

    2. In the Disk Utility sidebar, select the JBOD array you created earlier.

    3. To ensure you selected the correct item, check the Info panel. The Type field should read “RAID Set Volume.”

    4. Select the plus (+) button located above the Info panel.

    5. From the list of available disks, choose the disk or volume you wish to add to the JBOD array. Select Choose to continue.

    6. A window drops down, warning you that the disk you’re adding will be erased, causing all data on the disk to be lost. Select Add.

    7. The disk is added, causing the available storage space on the JBOD array to increase.

    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.

    1. Launch Disk Utility and select the JBOD array from the sidebar.

    2. Disk Utility displays the list of disks that make up the array. Select the disk you want to remove and select the minus () button.

    3. You are warned about the possible loss of data should the process fail. Select Remove to continue.

    4. After the removal is complete, select Done.

    Delete a JBOD Array

    You can delete a JBOD array, returning each disk that makes up the JBOD array to general use.

    1. Launch Disk Utility.

    2. Select the JBOD array from the Disk Utility sidebar.

    3. Make sure the Type field under the Info panel reads “RAID Set Volume.”

    4. Select Delete.

    5. A window drops down, warning you that deleting the JBOD array will likely cause all data in the array to be lost. Select Delete.

    6. After the JBOD array is removed, select Done.

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