My solution to a painfully slow iMac

(Feel free to skip this paragraph; it contains the obligatory tech specs but they are probably irrelevant to the problem at hand). I have a Retina 4K, 21.5-inch, 2019 iMac with 32GB of memory, a 3.2GHz 6-Core Intel Core i7, a Radeon Pro 560X 4GB graphics card, and a 1GB Fusion disk drive. The disk is not encrypted; it is only about 1/4 full. This machine is running Ventura 13.6.1 and I keep it and all of its apps completely up-to-date at all times. I purchased it new direct from Apple and I've been its sole user. Most of my work involves using Pages, Numbers, Quicken, Safari, Chrome, Zoom, MS Word, Excel, and Teams; pretty much in that order of decreasing usage. I use Carbonite and Time Machine for backup (yeah, I'm a little paranoid about losing files). My user files are in iCloud and I have a fast Internet connection (368 Mbps down, 10 Mbps up as of this moment). I'm also a professional software engineer with 50+ years of experience on large, commercial, transaction processing systems. I have a lot of experience with big systems but at home, I just want to use the thing, not debug it.

Over the last year or so, my iMac has gotten progressively slower and slower and slower, to the point where it would take seconds to draw the various elements of the windows. From boot to usability would take 12-14 minutes. Just loading Pages would take 1 to 1.5 minutes. Normally quick actions would take minutes. I leave this system running all the time, because I've learned that if I shut it down, performance is better than if I constantly reboot it. Not great, but better. Hardware test came up clean. I had to do something.

It became evident to me, after some experiments, after some research, and based on my experience, that the logical culprit was the Fusion disk drive. The symptoms matched what I might term as "SSD rot". SSDs are notorious for having their performance degrade over time, due in part to the way that operating systems must do a lot of writing to the same areas over and over. This report isn't the place to dig into these details, and I know that modern SSDs have tried to handle this cases better, but the ultimate solution is to trim the SSD and start over.

So that's what I did. I created a fresh Time Machine partition on my external RAID array. I let Time Machine do its thing and back up everything. I then took a deep breath, booted into the Recovery Partition and wiped out the user data volume, leaving only the recovery partition. I created a new user data volume (this may not have been necessary; Time Machine apparently would have also done this). I rebooted into the Recovery Partition and reloaded Ventura. I answered the usual initial configuration questions. I then reloaded all of the user files from the just-completed Time Machine backup. I'm delighted to report that my machine is back to its old self again. No more multi-minute waits for trivial tasks. From power on to usability is about twice as fast (6.5 minutes vs 10-12 minutes). Opening files, starting up applications, i.e. common operations, are all much faster. Sure, I'd like it to be even faster still, but at least the painfully slow behavior is gone now. I'm pretty sure performance is back to where it as when the machine was new.

One more thing; after the Hardware Test came up clean, but before I created the Time Machine Backup, I ran First Aid in Disk Utility, which found and fixed several errors in the system data. I try to run First Aid every few months but it had been a while. I was getting some mysterious crashes, and when that happens, First Aid is usually the cure. I don't think this had anything to do with the performance issues; but it did seem to eliminate the mysterious crashes.

I hope my story encourages others to try the same solution. It wasn't difficult but it did take me quite a bit of time because I wanted to be very careful and not make any mistakes. I won't wait so long next time things get painfully slow.