AntMonster wrote:
NOW, I'm staring at the "less than a minute to go" situation. It's been at least 45 minutes. There seems to be activity on the external drive. It's USB 3, and it's not a solid state drive, so I suppose this could slow things quite a lot. It's an empty 1TB disk so I'm sure it's not the problem with available space that I've seen people encountering.
Not surprising if using an external hard drive. Hard drives are very slow with a max transfer rate of 150MB/s at best, but usually more along the lines of 60-80MB/s or even less especially when using the APFS file system which tends to work the drive harder because the read/write heads must move around a lot when using an APFS file system.
Plus it is obvious the internal SSD has a problem of some sort which is very likely interfering even when booting to external media such as your external hard drive or Internet Recovery Mode.
I'll leave it running overnight if needs be, but at which point can it be accepted that the installation has failed? Some people have said that a reboot solves it (somehow). But to me that suggests just hitting the power button (there's no menu to restart from) - surely that's no good for the external drive? Thoughts?
Only you can decide when to force a power off. If the OS was fully copied when it got stuck, then rebooting will allow the system to start with phase 2 of the installation process.....sometimes you may need to Option Boot to select the external boot drive which may have a name such as "Install macOS" (not to be confused with a USB installer of a similar name).
You can remove the internal SSD & adapter in order to try to complete the macOS installation on the external drive. You can also remove the internal SSD to try performing another clean install of macOS to the external drive which may have a better chance at working if the internal SSD or adapter is causing problems.
What SSD adapter are you using with the third party SSD if it is an M.2 SSD? The Sintech SSD adapter is the only one I've seen on these forums which seems to be the most compatible & reliable. I've never seen anyone report any issues when using a Sintech SSD adapter, but I have seen almost every other brand of adapter reported as being problematic.
Plus not all SSDs are compatible with all computers, so there is always a chance the SSD may be incompatible.
Or the SSD may actually have a hardware problem. Once you get macOS installed & booting from an external drive, then you can run DriveDx to check the health of the internal SSD. Post the complete DriveDx text report here using the "Additional Text" icon which looks like a piece of paper so I can review it for clues since not all "Failing" or "Warning" conditions indicate a bad SSD....these reports need to be manually interpreted by someone familiar with interpreting SSD health reports. There are other ways of checking the health of a drive which I can provide if needed. Unfortunately most SSDs fail due to controller communication issues which do not show up in any health report.