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Released in July 2018, the 15" MacBook Pro, model A1990, features a 15.4 inch LED-Backlight display with True Tone technology, TouchID, and up to 6 Core i9 Processor.

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Why won't my MBP boot from the ext SSD

Had 2013 MBP that died.  Took out the SSD (with iFixit tools) and put it in an Other World Computing USB enclosure (Envoy).  Connects to new MBP 2018 via Other World Computing micro-b usb 3.0 cable with an Apple usb to usb-c adapter.  4 partitions (one aspf and three GUID Mac OS extended journaled) display on the screen and I retrieved the data that was not backed up so that all is well.  Running 10.13.5 and 6.

Then thought I would (for the fun of it) try to boot from the now external SSD.  Nope.  Fails.  See the circle with the line (ie no valid system). Have tried both command-R and system preferences.  Both offer it as boot option.  Have re-installed High Sierra.

Also Disk Utility says the drive is not solid state and is not bootable.

Other World Computing says I need a USB-C to USB Micro-B 3.0 and omit the Apple adapter so have ordered one but...

Why won't it boot?  And why does Disk Utility say it is not solid state and not bootable?

Is true, I retrieved my data so should give up, move on, but am now soaked in curiosity.

Answer this question I have this problem too

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The new 2018 models hav a T2 chip in them unlike older MacBook Pro’s. The T2 chip offers a higher degree of security! As such somethings are a bit harder unless you tell it not to do something. Here is a good Apple T/N which reviews the different security levels About Secure Boot your system has.

Click on the External Boot ‘Allow Booting from External Media’ should resolve your issue.

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7 Comments:

thank you but

is already set to allow ext boot and I have other ext drives that boot

also set to no security

will keep piddling with this

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Was the drive protected in some way?

You may need to send the drive out to someone who can recovery it as it might have been damaged.

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Thanks. The SSD drive shows on the desktop so I recovered all files. But now that I have it, I thought would try to boot from it. And cannot figure out how to make it boot reliably.

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Try this hold the Option key when you reboot the system that will allow you to gain access to the startup Disk manager, then select your external that should do it.

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Thanks but more than half the time it does not show up with Option boot, even if I connect the drive at the time the drive selection appears.

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Loren Engrav will be eternally grateful.
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