I'm trying to get a bootable hard drive with macOS Sierra going so that I can use Octane Render. My Macbook is running macOS High Sierra, which is apparently buggy with Octane at the moment.

I purchsed a WD easystore, partitioned it to be Mac OS Extended (Journaled), and put the macOS Sierra installer on it (I downloaded this from the App Store). First, I was starting up with that disk and continuously getting the following error message: "This copy of the Install macOS Sierra.app application is damaged, and can't be used to install macOS."

NOW I'm not even getting to that stage, the drive isn't even showing up as a bootable disk! When I go to System Preferences > Startup Disk, it's not even there as an option.

Please help me - getting verrrry frustrated as I have no idea what I'm doing. Thanks in advance!

  • You need to download an valid copy of the Install macOS Sierra.app from the App Store and create a macOS Sierra USB Installer on an 8GB Thumb-drive, then boot the Mac from the macOS Sierra USB Installer and install macOS Sierra to the WD easy store Portable Hard Drive. All the steps necessary to do this have already been covered on AD and the Internet. Google is you friend! Nov 27, 2017 at 17:25

2 Answers 2


Assuming that you don't have an additional thumb drive (according to Apple with at least 12 GB - I got it to work with a 8 GB thumb drive) I recommend the following method:

  • erase and repartition your WD easystore to two Mac OS Extended (Journaled) partitions - a bigger one first with the name "Sierra" and the size (total_size_of_external_drive - 12 GB) and a much smaller second one with the name "Sierra_Installer" and a size of ~12 GB. The partition scheme has to be GUID! If your MacBook's main partition already has the name "Sierra" choose another name for the first partition of the external drive. Below I assume the bigger volume on the external drive has the name "Sierra".

    Example: if your external drive has a size of 1 TB, then the first partition "Sierra" should have a size of 988 GB and the second "Sierra_Installer" partition one of ~12 GB.

  • re-download the "macOS Sierra installer.app" on your MacBook
  • open Terminal.app in /Applications/Utilities
  • enter the command:

    sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/Sierra_Installer --applicationpath /Applications/Install\ macOS\ Sierra.app

    hit the Enter key, enter your password (which won't be visible because it's masked), hit the Enter key again and let do createinstallmedia its job.

  • Quit Terminal after the job is done and any other app.
  • Reboot to "Sierra_Installer" (e.g. by choosing it in System Preferences > Startup Disk or by hitting the alt-key while booting and choosing Sierra_Installer)
  • After a successful boot of the "Installer Boot Partition" install macOS Sierra to the volume "Sierra".
  • After a successful installation configure Sierra.
  • Finally remove the partition "Sierra_Installer" with Disk Utility and resize the volume "Sierra" to the full size of the disk.

The method proposed by user3439894 in a comment to your question is preferred though: create an Installer Thumb Drive, boot to it and install Sierra to a single-partitioned external drive.

  • @user3439894 No, the installer_volume has a size of 12 GB! The volume to install the OS to has a size of (total_size - 12 GB). Seems to be unclear!
    – klanomath
    Nov 27, 2017 at 19:35
  • At first I didn't see it as a mathematical formula. :) I'd probably would have written/worded that differently but nonetheless it's a good answer and alternate method that will work. Nov 27, 2017 at 19:48
  • THANK YOU! This worked. Can't thank you enough, this was doing my head in. Cheers! Nov 29, 2017 at 14:55

Take a copy with Carbon Copy Cloner

  1. Boot MacOs High Sierra from Mac.
  2. Format WD EasyStore to "Mac OS Extended" using Disk Utility.
  3. Use a bootable backup software such as CCC5 to copy the drive you are currently booted from onto the WD Easystore
  4. Restart, when you hear the startup sound hold 'alt' or 'opt'
  5. Choose WD EasyStore as boot drive.
  • The OP wants to install macOS Sierra not macOS High Sierra on the WD easystore Portable Hard Drive, so your answer is not applicable and therefore a wrong answer to what was asked in the OP. Nov 27, 2017 at 17:19
  • @user3439894 Unless the software mentioned doesn't run on MacOS Sierra, than it's just a harmless typo and it can be corrected.
    – Matthew N
    Nov 27, 2017 at 19:30
  • @Matthew N, The OP stated "Macbook is running macOS High Sierra, which is apparently buggy with Octane at the moment." So cloning macOS High Sierra is not the answer when the OP is trying to install macOS Sierra on an external drive to use Octane on it then under macOS High Sierra. I suggest you re-read the OP! Nov 27, 2017 at 19:36
  • @user3439894 My bad, I didn't read it right the first time.
    – Matthew N
    Nov 27, 2017 at 19:42
  • My bad 😅 I also misread it Dec 3, 2017 at 12:41

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