How to create an external Mac startup disk for macOS High Sierra

“If you install the Mac operating system on an external hard drive, thumb drive, or other storage device, your Mac can start up from that device instead of your built-in startup disk,” Dennis Sellers writes for Apple World Today.First, make sure that your storage device is properly formatted.”

“For best results, your external hard drive, thumb drive, SDHC or SDXC card, or other storage device should be formatted as Mac OS Extended, not FAT, ExFAT, or NTFS,” Sellers writes. “And to function as a startup disk, it needs to be using a GUID partition map.”

Sellers writes, “The installer needs at least 8GB of available storage space.”

Read more in the full article here.

MacDailyNews Take: Creating an external Mac startup disk is simple and it’s the best way to mess around with macOS betas when you don’t have a dedicated test Mac at hand.


  1. One way that I like to play around with other macOS configurations – including betas – is to use Parallels Desktop Lite, which is a free VM hypervisor product from the folks that brought you Parallels Desktop, arguably the most popular VM product for Macs.

  2. Saved me a last month when my hard disc went awol. Thankfully because I wanted to test Sierra with all my software I set it up on an external last Oct and was able to use that until I could get the Mac fixed. A couple days interruption to my work flow as a result while it was away fitting a new upgraded SSD.

        1. The point was that you clicked on a story you already knew about so you can brag about how superior you are to everyone else.
          The “point” is that you are an ass.

          1. Really. You got up this morning and your life is so pitiful and pathetic that you go out of your way to try…. operative word is try…. to what.. make me feel bad or something. I have something for you. Shut.Up.

            You must really like ass.

            1. I see you are the type of person that likes having the last word.
              Oh, and don’t try to pretend that you know what other people know and don’t know. You’d be wrong.

  3. One way you can boost the speed of a Mac mini is to use an SSD as the boot disk. It gets around the slow assed 5400 RPM HD inside. I keep a mini in the LR and do this via USB 3.
    You can use the internal as a backup.

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