iMac's Fusion Drive SSD Failure

Just about 5 years ago now, I purchased a 4.2GHz 27-inch iMac with a 3TB Fusion Drive. I opted for the Fusion drive due it being the most amount of storage that I could get at the time and besides that SSD prices were, and still are, a bit much for the same amount of storage.

With a Fusion Drive it is actually two physical drives. In my case a 128GB Solid State Drive and a 3TB 7200 RPM traditional spinning hard drive. These two drives are logically connected to be presented as a single drive to macOS. The SSD portion would store the operating system files as well as the most commonly used files and data, to provide it the fastest access possible, meanwhile everything else would be stored on the traditional spinning hard drive.

Back in April I purchased a Mac Studio and the Mac Studio is now my primary computer. I opted to get the Mac Studio after the screen on my iMac began to crack. It started as a small 1-inch crack but it since expanded quite a bit, to be 18-inches. As a side note, the crack has not expanded at all, which I find interesting. Since the iMac has been replaced, I was only being used as a device to test out the macOS Ventura betas.

I went to install macOS Ventura developer beta 3, but the update never installed, at least I do not think it did. When I went to check on it the screen was entirely black. The machine was still running because the backlight of the iMac screen was on. So, I held down the power button to force the iMac to turn off. I waited a bit, turned it back on and let it boot. Once at the login screen I went to login, but as soon as I attempted to actually login, the entire system just froze giving the infamous beachball.

Knowing that there was obviously something wrong, I rebooted into Recovery Mode and ran First Aid on both drives and their APFS containers. If I scanned each one of them on its own, they would both pass. Having both of them passed, I figured it might just be a software problem and re-installing macOS should fix it. I attempted to re-install macOS Ventura, but it presented me with an error that stated that the drive failed with some S.M.A.R.T errors. Typically, when drives have S.M.A.R.T. errors, that means that the device is failing.

This left me with a bit of a quandary. I have an external SSD that has macOS Monterey on it. So, I attempted use that to run Disk Utility and received the same results. It passed the First Aid checks. I thought it could be an issue with the Ventura beta, so I attempted to re-install macOS Monterey. But that also failed with the same S.M.A.R.T. error message. No matter what I did nothing would install. I was still able to access all of the data, which was all on the spinning hard drive.

Ultimately, what I ended up doing was erasing the spinning hard drive and re-partitioning it. After it was partitioned I re-installed macOS Monterey. This worked, because the spinning hard drive did not show any S.M.A.R.T. errors. After it finished the macOS Monterey install, I did the initial setup then I attempted to upgrade to macOS Ventura, but it sat there on 48 seconds remaining for who knows how long. So, I rebooted the iMac and restarted the installation.

The Ventura beta installation did complete and my 2017 iMac is back to working condition, albeit a bit slower than before. That is to be expected though, given that it is a 7200RPM hard drive that is now being used, even for system files. The slowness is acceptable though since it is just for testing and not my daily machine.

Regardless of type of drive, is that they will fail eventually. With that, the one thing I find interesting is the fact that SSD failed before the spinning hard drive. If the spinning hard drive fails, I will likely just hook up the external SSD again and use that. I briefly thought about possibly opening up the iMac and replacing both drives with a single SSD, but it is a lot more work than it is worth, and the procedure to do so, while possible, seems rather daunting.