External USB don't show on boot

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Level 1

9 points

External USB don't show on boot

I have an external USB SSD install with Windows 10.

On my MacBook Pro 15" mid 2014 I can press option on boot and it will show up and I can boot to Windows.

However when I try on my MacBook Air 13" early 2015, pressing option on boot doesn't show up the external USB SSD, only macOS partition is shown. When I boot in to macOS, I can view the external USB thus the USB port is not faulty, I also try again on my MacBook Pro and its able to boot up to Windows with no problem

How to access it on my MacBook Air? I tried on both USB ports doesn't work.

The only different is on my MacBook Air I turn on FileVault which is require by my company while the MacBook Pro don't as I use at home.

Any help is appreciated. Thanks in advance.

MacBook Air, Mac OS X (10.7.5)

Posted on Mar 12, 2017 10:44 PM

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Answer 1

Best reply

cavemees

Level 4

1,646 points

Mar 14, 2017 6:23 AM in response to Spoon79

Your external disk has a MBR partition scheme. A Mac can't boot from a MBR disk and needs a GPT partition scheme to be able to boot from; "And to function as a startup disk, it needs to be using a GUID partition map." from support page: How to set up and use an external Mac startup disk - Apple Support

I can't explain why you're able to boot from it with your MacBook Pro, it shouldn't as far as I know...

You started this post in the MacBook Air category. The issue is related to Windows/Bootcamp, I would suggest two options:

I can ask the 'host' to move this post to Windows Software / Bootcamp category.
You start a new post with the specific issue in Windows Software / Bootcamp and refers to this post.

Experienced users with Windows/Bootcamp will pickup the post more likely in the Bootcamp categoy then here. Let me know what you do/want.

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Answer 2

cavemees

Level 4

1,646 points

Mar 13, 2017 8:11 AM in response to Spoon79

See section "If you can't select your startup disk or start up from it" for possible reasons why you experience different behaviour between you Pro and Air: How to set up and use an external Mac startup disk - Apple Support

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Answer 3

cavemees

Level 4

1,646 points

Mar 14, 2017 4:37 AM in response to Spoon79

Try the drive in other USB port on your MacBook Air.

Try resetting the NVRAM: How to reset NVRAM on your Mac - Apple Support

You have only FileVault enabled and not set a firmware password? ( Use a firmware password on your Mac - Apple Support )

Is the drive visible and are you able to set it as startup disk in: System Preferences > Startup Disk ?

I assume you installed Windows using Bootcamp on your MacBook Pro?

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Answer 4

Spoon79 Author

Level 1

9 points

Mar 14, 2017 5:05 AM in response to cavemees

I tried reset nvram, also use other port, I even test another bootable USB but it can be detected, just the external windows 10 USB drive not detect on MacBook Air during boot, but once boot in macOS It show up as external drive.

only filevault enable no firmware password etc.

Drive is visible in startup disk but when I click restart it say unable to bless the disk and I am not able to proceed to restart perhaps this is the problem?

my MacBook Pro don't have bootcamp install, only use the external ssd to use windows.

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Answer 5

cavemees

Level 4

1,646 points

Mar 14, 2017 6:46 AM in response to Spoon79

I have no experience with a Windows setup as you have and I have no more ideas to try. We have also no answers from other users in this MacBook Air category. Chances are that users follow the Bootcamp category (and not looking here) do have an answer for you, see my suggestion in previous post.

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Answer 6

Drew Reece

Level 6

10,660 points

Mar 14, 2017 11:22 AM in response to Spoon79

FYI, some Macs can boot from MBR disks - it is called 'legacy boot' it depends on the model & has been phased out since EFI & GPT (GUID) disks have become the norm on other OS's. Perhaps the Air is too new to support that mode.

I don't know if the Air is able to boot Windows from an external disk, it seems likely that the MBR is the reason for it failing but some Macs are very fussy when trying to boot other OS's from external drives.

I'd look at setting up rEFInd – http://www.rodsbooks.com/refind/ possibly on another partition of the Windows OS disk (or on a separate USB stick). It may be able to 'chain load' into the Windows system.

Frankly it may be easier to setup a VM on the Air or install Windows via bootcamp. That way the Windows OS will have the correct EFI/GUID support. I'm also not certain that one Windows OS will always boot a different model of Mac due to different drivers.

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Answer 7

Spoon79 Author

Level 1

9 points

Mar 14, 2017 5:00 AM in response to Spoon79

just try on my MacBook Pro it show the same problem too but still I am able to see it during boot up and boot into windows.

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Answer 8

Spoon79 Author

Level 1

9 points

Mar 14, 2017 5:02 AM in response to Spoon79

This is the external drive info

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Answer 9

Spoon79 Author

Level 1

9 points

Mar 13, 2017 7:13 PM in response to cavemees

I tried all the steps in your link but still not showing up in my MBA. Still my MBP work perfectly with the external SSD running windows 10

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Answer 10

Spoon79 Author

Level 1

9 points

Mar 14, 2017 6:31 AM in response to cavemees

I just test the external hdd on my wife's MacBook Pro 2012 non retina, it show up during boot as well... now just the MacBook Air don't show up on boot.

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