RAID 10 Using Mac Disk Utility

Set up a RAID 10, Striped Set of Mirrors, using Mac OS X Disk Utility

The purpose of this series of articles is to provide some documentation on the use of Mac OS X Disk Utility.  A previous post demonstrates the need for this documentation increases as more new storage devices show up on the market requiring the use of Disk Utility to implement RAID.  The new devices requiring Disk Utility include: the Promise Pegasus J4, the LaCie 5big Thunderbolt, and the USB 3.0 hub RAID, to name a few.  This article will cover the creation of RAID 10 a “striped set of mirrors” using Mac OS X Disk Utility.  A previous article covered setting up a RAID 0 striped set using Mac OS X Disk Utility..

The reasons for creating a striped RAID set include maximizing the speed and capacity of two or more disks by combining them into a single volume. The reason for creating a RAID 1 mirror is to increase data redundancy thus decreasing the chance of failure because of a disk drive failure. The reason for creating a RAID 10 stripe of mirrors is provide more capacity and speed than a single drive can provide and all of the redundancy of a RAID 1 mirror.

The reasons for not creating a RAID 10 set include reduced capacity and speed from RAID 0 alone and reduced potential redundancy from RAID 1 alone.  RAID 10 can be, at most, one half the capacity of a RAID 0 array. Four drives configured in RAID 1 provides 300% redundancy with all four drives being a mirror of each other, while the same 4 drives in RAID 10 provide only 100% redundancy with two mirrored pairs striped together.  With a 4 drive RAID 1 you can loose any 3 drives and still retain your data.  With a 4 drive RAID 10 you can loose 1 drive from each mirrored set and still retain your data.

Step by step instructions:

Attach all drives to be included in the RAID 10 array to the computer.  Raid 10 requires at least 4 drives.

Start Mac OS X Disk Utility. (To find Disk Utility, simply click the magnifying glass in the upper-right corner of the Mac screen and type in “Disk Utility”.)

Ensure all drives to be included in the striped set are visible in Disk Utility.

If any drives were previously part of another raid you may have to “Erase” the drives first.

Select any one of the drives to be included in the striped set and then choose the “RAID” button.  Ensure

Format: Mac OS Extended (Journaled)

RAID Type:  Mirrored RAID Set

Press the “+” button for each mirrored set you wish to create. For 4 total drives you will press the “+” button twice.  For 6 total drives you may press the “+” button 3 times for 3 pair of mirrors, or twice for 2 sets of 3 drives in a mirror.

Name each set appropriately. (i.e.: “Mirror 1, Mirror 2”)

RAID 10a Mirrors established

Press the “+” sign once more ensuring:

Format: Mac OS Extended (Journaled)

RAID Type:  Striped RAID Set

RAID 10b RAID sets established

Drag and drop each drive to their appropriate Mirrored RAID set.

RAID 10c Mirrors setup

Drag and drop each Mirrored RAID set underneath the Striped RAID set.  When done properly each of the Mirrors will we indented from the Striped RAID set.

RAID 10d Setup Ready to Create

For each Mirrored RAID set press the “Options” button and select “Automatically rebuild RAID mirror sets”, if desired. If you are not sure, select it.

RAID 10e Mirror Options

Press the “Create” button.

When complete, Disk Utility will mount the new drive and the new drive will be visible on your desk top just like any other drive.

RAID 10f Build Complete

In the event a drive becomes disconnected there will be no effect on the system.  Work will progress as before. If the drive becomes reconnected the Disk Utility will start a background process that will automatically rebuild the disconnected drive.

In the event a drive fails and must be replaced an automatic rebuild will not occur.  To force a rebuild perform the following steps:

Attach the new drive to be included in the RAID set to the computer.

Start Mac OS X Disk Utility.

Select the degraded mirror from the list of drives and RAID sets on the left so that it appears in the window on the right.

Drag and drop the new drive into the degraded mirror.

RAID 10g Add new drive to Mirror for rebuild

Press the “Rebuild” button.

RAID 10h Rebuilding Mirror 2

For the purposes of this demonstration we replaced 2 drives, one from each mirrored set.

RAID 10i Rebuilding both mirrors

It will be awhile! Do not be alarmed, it is running in the background and should not affect your work.

RAID 10j rebuilding both mirrors It will be awhile

9 thoughts on “RAID 10 Using Mac Disk Utility

  1. Felipe

    This was extremely helpful and the RAID 10 we built has served us well for many months.

    Now however, we’d like to dismantle this RAID 10 array so we can use this same enclosure and drives to build a different RAID using SoftRAID… data loss is not a concern as we’ve already copied everything over — but I can’t figure out how to disassemble this existing raid and format the individual drives!

    Any tips?

    Many thanks!

  2. sharpcocoa

    Thanks of the article. Just what I was looking for. I have an additional question that have not been able to find an answer for. Is there any way to progressively expand an array like this? Say when the first 3TB drive fails replace it with a 4TB? I know you would have to keep them balanced, i.e. have maybe one 4TB and one 3TB drives in each mirror. What happens if you replace one drive in a mirror with a higher capacity and after it rebuilds replace the other in the pair with a matching higher capacity drive?

  3. Jim


    a tutorial to show how to rebuilt a defective HDD would be fantastic once the raid 1+0 is configured

    thanks a lot

  4. Janus

    I have tried doing three mirrored sets (which works fine). However I can’t seem to add all three sets (6 harddrives) into one striped set. Any suggestions?

    1. admin Post author

      Unfortunately, I think you will have to set up the whole thing at one time, that is, define the mirrors and the stripe of the mirrors during set up and then let the disk utility do its thing. It will not take a series of existing mirrors and stripe them.

  5. Mark Thomas (@mark00thomas)

    Is this still considered RAID 10: I have 2 LaCie 5big drives. I think I want to stripe 4 disks from each and have them mirror each other. Each letter below is a drive in the LaCie box. This should give me 16TB of RAID 10 and two extra drives.


    Striped <— Mirroring the first strip

    1. admin Post author

      Mark, Yes, that is an implementation of RAID 10. What are you using for backup? Another thought would be to configure all drives in each box in RAID 0 then use the one box as your time machine backup drive and leave it connected. I believe the need for frequent backups is much greater than the need for redundancy. The primary advantage of RAID redundancy is to ensure that the system stays up in case of a disk crash. This is very important for multi user systems that can not afford any downtime. Once you replace the bad disk recovery can take days, running in the background. Over the last decade I have had 1 hard drive failure. Over the last decade I have needed to recover overwritten/deleted/corrupted files at least once a year. My backup saved the day in each case, redundancy would have only helped for the disk drive crash. If speed is a consideration (and considering your investment, it is) backups will only run when it does not affect your work, any RAID greater than 0 will run slower than RAID 0.

    1. admin Post author

      Francesco, as it happens there were no step by step instructions with screen shots out there, so we published them. Thanks, Mike


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