I just got a 2015 13" 16gb RAM machine and put a 1T drive I had in it (it's very easy to do -- takes 5 minutes). Then, when I tried to boot up, it did not recognize the drive. I was worried about some sort of hardware inconsistency with the SSD, but finally realized that my SSD was formatted by High Sierra in APFS while the SSD that came with the machine was running Sierra and used the older file system. When I booted off the 256Gb drive that came with the computer as an external disk and upgraded that to High Sierra, I was able to boot off the 1T SSD. This means that when you upgrade to High Sierra, something in the computer's ROM is modified so that it can recognize the new file system and boot from it.
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Important if you buy a used MBP and replace the ssd
- Thread starter glhiii
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Are you sure you can't just boot with the option key held down, pick your SSD, then use System Preferences to set your startup disk and reboot? I doubt the ROM is modified in any way.
Installing High Sierra does require an upgrade of the EFI if the computer doesn't already have an High-Sierra compatible EFI. Some of the EFI updates went out before High Sierra was officially released. I haven't seen an Apple publication to this effect, but that seems to be the case. From the paper that Duo Labs did about the EFI, they mention this. An excerpt from the paper is as follows:
"In order for the early boot environment to be able to mount an APFS volume, an “ApfsJumpStart” DXE driver was added to Apple’s EFI environment."
https://duo.com/blog/the-apple-of-your-efi-mac-firmware-security-research
A lot of the EFI's for different computer/OS combinations were updated via the regular software update procedure to include High Sierra compatibility as well as security reasons. On my 2012 Mini running El Capitan, it was updated at some point to use the EFI needed by High Sierra. I believe my mid-2012 MBP running Sierra was similar upgraded.
If you recently purchased a computer that may have been sitting on a shelf someplace for the past few months, it's possible that the OS update with the EFI update was not run. Or (and this was a big point of the Duo Labs paper), for whatever reason, it seems that some Macs have issues with EFI updates but this isn't necessarily communicated to the user. Or perhaps the previous owner just ignored running updates.
If you have an OWC Aura SSD, there were issues there with High Sierra although OWC claims it didn't affect the MBP - I don't know all the details there.
So yes, if you want to install High Sierra, you need a compatible EFI. Apple doesn't make this easy as the last time I checked, they stopped updating the article they had which listed the latest EFI version for each Mac.
"In order for the early boot environment to be able to mount an APFS volume, an “ApfsJumpStart” DXE driver was added to Apple’s EFI environment."
https://duo.com/blog/the-apple-of-your-efi-mac-firmware-security-research
A lot of the EFI's for different computer/OS combinations were updated via the regular software update procedure to include High Sierra compatibility as well as security reasons. On my 2012 Mini running El Capitan, it was updated at some point to use the EFI needed by High Sierra. I believe my mid-2012 MBP running Sierra was similar upgraded.
If you recently purchased a computer that may have been sitting on a shelf someplace for the past few months, it's possible that the OS update with the EFI update was not run. Or (and this was a big point of the Duo Labs paper), for whatever reason, it seems that some Macs have issues with EFI updates but this isn't necessarily communicated to the user. Or perhaps the previous owner just ignored running updates.
If you have an OWC Aura SSD, there were issues there with High Sierra although OWC claims it didn't affect the MBP - I don't know all the details there.
So yes, if you want to install High Sierra, you need a compatible EFI. Apple doesn't make this easy as the last time I checked, they stopped updating the article they had which listed the latest EFI version for each Mac.