How to install High Sierra on an OWC Aura N-Series SSD in a MacBook Air 6,2 without an existing hard drive?

AFAIK, loading High Sierra onto the SSD first and then installing it into the MBA will not work. the MBA must have been updated to High Sierra at some point in its life. the firmware EFI gets flashed to said Mac, not the SSD. and without the proper firmware, the SSD blade will not be recognized without the firmware being present.

If this laptop has never previously had macOS 10.13+ installed , then the only way to do so now is by reinstalling the original Apple OEM SSD internally. All macOS 10.13+ installers require a working properly formatted internal drive in order to update the system firmware. Once the system firmware on the laptop has been updated, then you can easily install the OWC SSD into the laptop and install macOS 10.13 to 11.x onto it.

If you have a 2015 MBAir, then in order to install macOS 12.x Monterey.....you will need to once again have the original Apple OEM SSD installed internally. Unfortunately the Monterey installer has an additional requirement of needing the internal Apple OEM SSD or the Monterey installer will refuse to install the system firmware update.

Unfortunately I'm not aware of any third party SATA based PCIe SSDs that are compatible with a 2013-2017 MBAir other than an Apple OEM SSD. Finding an Apple OEM SSD that is compatible with that laptop is difficult. Apple has several different versions of the SSD for various Apple computers utilizing this exact proprietary PCIe SSD connector. Even though they can physically fit and work with a non-Apple OS......macOS may not even boot if the incorrect SSD is installed. This is from personal experience.

The reason you cannot use the OWC SSD right now is because the third party SSD is an NVMe based SSD whereas the original Apple OEM SSD was SATA based. The system firmware included with macOS 10.13+ provides the ability for the system to both recognize an NVMe based SSD and to work with the APFS file system. All third party SSD PCIe options for this laptop are NVMe based SSDs (most requiring a special adapter) so there are no other options.

Unfortunately all of these macOS 10.13+ installers require the system firmware update to be staged from the internal SSD.

I did stumble across instructions a few years ago to allow the system firmware update from the Monterey installer to be used from an external drive, but it required the system firmware to be at a specific version or it would not work. I have never seen any similar instructions for macOS 10.13 or any other OS although the same technique should work barring any specific minimum firmware requirements. So this probably is not a viable option either.

tadtadtadtad wrote:

So if I understand you correctly I would need a very specific Apple OEM SSD that would be a perfect fit for my MBA

Yes. It is not just about having the proper physical connector, but also a drive that macOS itself will recognize as belonging to that exact model Mac.

that also has not yet been updated to macOS 10.13+ in order to allow the Apple update software to flash the EFI Boot ROM while it's upgrading to macOS 10.13+ (the 'while it's upgrading' part feels like my imaginings rather than your explanation) but other than that, am I on the right track in my understanding?

This doesn't matter. You can just erase the Apple OEM SSD (GUID partition and MacOS Extended (Journaled) ) and the macOS 10.13 or 10.14 installer will be happy. I don't know if the macOS 10.15, 11.x, or 12.x installer will work until the system firmware has been updated since they require the APFS file system for installation although Catalina did at one time automatically convert the file system.

If I am following you, then only when I've completed upgrading 10.13+ would I be able to successfully install an NVMe based SSD after several more steps. Is that correct?

Correct. At least for any version of macOS up to 11.x Big Sur the installer should not care if a third party SSD is installed internally in respect to system firmware updates.

If you have the 2015 model, then the macOS 12.x Monterey installer requires an Apple OEM SSD to be installed internally in order to update the system firmware. So I would recommend first installing macOS 10.13, then upgrade to macOS 12.x Monterey. Theoretically you should be able to just install macOS Monterey since the App Store lists the minimum OS as 10.9 for installing Monterey.

Once the system firmware has been updated, then you should never need the Apple OEM SSD again unless you use it to troubleshoot the system if you think the OWC SSD is having an issue.

Also, to help my understanding, what part of this process or which of these steps prevents the SSD in the external enclosure from being upgraded beyond 10.11+? It seems to follow that if a computer can boot up and be run from an external SSD that it should be able to update the operating system on that external SSD if the cpu is compatible with more recent operating systems. Please let me know where and what holes are in my nascent upgrade logic.

As you have found out, you can easily use the NVMe SSD externally as a boot drive with macOS 10.11 since the SSD's NVMe controller does not require any macOS support since the external enclosure takes care of that part of the equation. macOS only cares about the external enclosure when communicating with the external SSD since it is using the USB protocol to communicate which older versions macOS understand. When installed internally macOS needs to communicate with the SSD directly using the NVMe protocols which only macOS 10.13+ understand.

The macOS 10.13+ installers force a system firmware update unlike the older macOS installers (or perhaps those older installers allowed the system firmware to be updated from an external drive). I have no idea how the older installers behaved, but I do know Apple wanted to ensure macOS 10.13+ always started at a specific firmware version since many systems were not updating their system firmware during macOS update patches. Once the system firmware is the same or newer than the installer's bundled firmware, then that particular installer will no longer attempt to update the system firmware on subsequent installations since it is not necessary. This is why there is no problem reinstalling macOS onto the internal third party NVMe SSD later on.

I am very grateful and thankful for the help.

You're welcome. Unfortunately this is complicated & confusing to explain. I hope this makes sense.

FYI, to get the exact model of your MBAir, you can get that information by clicking the Apple menu and selecting "About This Mac". Unfortunately the MBAir 6,2 designation applies to models from 2013 to 2015. While these Airs are almost identical, there are some important differences especially with the 2015 model.