Error Reinstalling macOS Sequoia

Since Monterey is already running on the replacement SSD, the Mac is basically proving that the hardware and basic boot chain are functional... the interesting part is that Sequoia fails during installation, which points more toward the APFS/container or installer/firmware handoff than the old Fusion Drive itself.

I would stop trying the GUI upgrade and first download the complete Sequoia installer with softwareupdate --fetch-full-installer --full-installer-version 15.7.9 (or another listed 15.x build), then run that installer from a freshly booted Monterey system..... if that still fails, boot from a USB created with createinstallmedia and inspect the SSD in Disk Utility with View > Show All Devices, because you want the physical SSD using GUID Partition Map with a clean APFS container, not an old Fusion/APFS layout or leftover Preboot/Recovery volumes.

The exact failure is also worth pulling from /var/log/install.log or log show --predicate 'process == "installd"' --last 2h, because Sequoia's installer will usually tell you whether it is failing at APFS conversion, Preboot creation, firmware validation, bless/boot volume selection, or package verification.

Given that Monterey was installed successfully by the shop, I would especially suspect the existing volume/container state or the particular Sequoia installer path rather than immediately assuming the new SSD is bad.... if a clean USB installation onto a freshly initialized APFS container fails at the same stage, then I’d start looking at the SSD itself, its firmware/SMART status, or an underlying hardware/firmware issue.

Thanks for your detailed reply.

It turned out my problem was dodgy RAM, I have 128GB of ECU RAM installed with a number of years and this was causing a glitch, once I swapped this out for the original 32GB of RAM macOS Sequoia installed.

That Mac should run up to macOS 15 Sequoia.

What do you see if you paste this to Applications/Terminal.app...

softwareupdate --list-full-installers

...if you see Sequoia installer, download it to /Applications with something like (might be 15.8.1 soon so wait for it because it might fix raw image glitch in 15.8 ... or download the earlier 15.x version):

softwareupdate --fetch-full-installer --full-installer-version 15.8

Zurarczurx wrote:

Sorry to hijack the thread but I'd like to download a Sequoia installer just in case. When I enter the

softwareupdate --fetch-full-installer --full-installer-version 15.8

I get a message "Installing" and the %age. I just wanted to confirm that this command only downloads the installer and won't go on to install it.

...hmm right now I'm on a M Mac that does not support Sequoia so I can't test that ...but maybe Apple has removed that raw-buggy 15.8 version. What download options do you get from:

softwareupdate --list-full-installers

...IMHO "Installing" in there is a bit misleading because it is just downloading, and even the App Store download install can then be just quitted.

Understood on the "installing" ambiguity.

I have never noticed that '%age' -- where did you see that, maybe a temporary glitch? Sometimes booting to safe mode fixes these install issues.

Hi.

Sorry to hijack the thread but I'd like to download a Sequoia installer just in case. When I enter the

softwareupdate --fetch-full-installer --full-installer-version 15.8

I get a message "Installing" and the %age. I just wanted to confirm that this command only downloads the installer and won't go on to install it.

Software Update found the following full installers:

* Title: macOS 27 Golden Gate, Version: 27.0, Size: 17969056KiB, Build: 26A428, Deferred: NO

* Title: macOS Tahoe, Version: 26.7, Size: 17951133KiB, Build: 25G229, Deferred: NO

* Title: macOS Tahoe, Version: 26.6.2, Size: 17953734KiB, Build: 25G83, Deferred: NO

* Title: macOS Tahoe, Version: 26.6.1, Size: 17938060KiB, Build: 25G76, Deferred: NO

* Title: macOS Tahoe, Version: 26.6, Size: 17942836KiB, Build: 25G72, Deferred: NO

* Title: macOS Tahoe, Version: 26.5.2, Size: 17875271KiB, Build: 25F84, Deferred: NO

* Title: macOS Tahoe, Version: 26.5.1, Size: 17872095KiB, Build: 25F80, Deferred: NO

* Title: macOS Sequoia, Version: 15.8, Size: 15296950KiB, Build: 24H23, Deferred: NO

* Title: macOS Sequoia, Version: 15.7.9, Size: 15289021KiB, Build: 24G830, Deferred: NO

* Title: macOS Sequoia, Version: 15.7.8, Size: 15288760KiB, Build: 24G824, Deferred: NO

* Title: macOS Sequoia, Version: 15.7.7, Size: 15288576KiB, Build: 24G720, Deferred: NO

* Title: macOS Sonoma, Version: 14.8.9, Size: 13334756KiB, Build: 23J631, Deferred: NO

* Title: macOS Sonoma, Version: 14.8.8, Size: 13333989KiB, Build: 23J620, Deferred: NO

* Title: macOS Sonoma, Version: 14.8.7, Size: 13336094KiB, Build: 23J520, Deferred: NO

Understood on the "installing" ambiguity.

Sorry - I meant the "1%" downloaded indication.

Zurarczurx wrote:

Sorry - I meant the "1%" downloaded indication.

oh, that is just the download progress indicator which goes up to 90% (sic) until it finishes.