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How do I make a boot disk?

If you are running OS X El Capitan (10.11) or earlier, choose “Create Boot Disk” from the “iPartition” or “iDefrag” menu and follow the instructions. You will need to be running iDefrag 5.1.3 or earlier, or iPartition 3.5.1 or earlier, as later versions have had the “Create Boot Disk” option removed as it was not possible to make it work with macOS 10.12 or later. There is no point trying these older versions on macOS 10.12; the “Create Boot Disk” option will not work on 10.12 because of changes Apple made to the recovery partition.

If this does not work, or you are running macOS Sierra (10.12) or later or a newer version of iDefrag or iPartition, please follow the instructions below:

  1. Obtain a suitable boot device. A USB stick of 32GB or more in size is suitable, or you could use an external hard disk.

  2. In the Mac App Store, on the right hand side of the “Featured” page, under “Quick Links”, you should see a link to the latest version of the macOS (at the top). Click it.

  3. Click the Download button to download the macOS installer.

  4. Run the installer.

  5. Click “Continue”, then agree to the license agreement.

  6. Choose your boot device from the list that appears, and click “Install”.

  7. When prompted, restart from your boot device and complete the install.

  8. We recommend that you change the desktop background on your new boot device to one that you wouldn’t normally use, so that you can easily tell you are booted from something other than your normal boot device.

  9. Install iDefrag, iPartition, and/or any other utility software you want to use, on the new device.

We also recommend that you leave your Boot Disk setting in System Preferences set to your usual boot device, then start from the new boot device by restarting and holding the Option (⌥) key when you hear your Mac’s boot chime.

USB Stick Partitioning

USB sticks on which you propose to install the macOS need to be partitioned using a GUID Partition Table. This is easy on older versions of the macOS — you can just use Disk Utility to partition the USB stick appropriately. Unfortunately on newer versions (High Sierra in particular), Disk Utility doesn’t offer to place a partition table on USB sticks. As a workaround, you can repartition the USB stick from Terminal; first, you need to determine the device name, which you can see next to “Device” in Disk Utility:

What you see in Disk Utility when you select a USB stick

In the case above, the device name you need is the first part — disk5. You don’t need the s1 part on the end.

Then, in Terminal, enter

diskutil eraseDisk JHFS+ "Boot Disk" GPT disk5

replacing disk5 with the device name from the window.

Posted by alastair at 2016-Dec-28 11:12:03 UTC. Last updated 2018-Feb-15 11:02:38 UTC.