Very slow boot on Fusion and Big Sur

Thank you, but you haven't read the (admittedly) long thread completely, as it appears.

We have booted in safe mode, months ago already.

No login items are present, no launch daemons, no launch agents that can be called suspicious or unnecessary.

I'm willing to give step 3 a try, but I suppose you mean to move the cache files and the "saved application state" files to a new folder and then erase the original ones?

And Apple Care has been contacted before. In my case they were very helpful and put me through to a Senior Support Engineer, who confirmed that our problem had been acknowledged and was being looked into.

The last thing should can try is to create another user on your Mac and to try to boot and log on with the newly created user. If the boot time is far lower than usual, it means that your original profile it quite messy. In that case you can move the documents to the new profile and then delete the original one. In this way you don't have to reinstall all the applications. The only drawback is that you'll lose all the application settings and preferences (but in some cases it's also possible to move them to the new profile).

Yes, thank you. I already did that a few months ago, with a previous version of Big Sur. It didn't change anything to the boot time. I may try it again on 11.3, or actually since this morning 11.3.1 already...

I've really checked everything I could concerning my account, even displaying potentially disturbing hidden files and folders. Nothing seems to be wrong.

As I said, with 11.3 boot time has improved on my system also, but only marginally. As soon as I added apps and data to the newly created account, the boot time went up, from around 25 seconds to 2m30s or more before having a responsive desktop and Finder. I have about 520 GB of free space left on my 1 TB Fusion Drive. That's certainly not a problem, but it is far less than what you and Tomeranaray have stored on your iMacs. As I have reported a few months ago, with a previous version of Big Sur I was also able to boot my iMac in 20 seconds, with a newly created, empty account, but simply adding a few apps like Pages, Numbers, Keynote, and especially iMovie made the boot time climb up to 1 minute or more immediately. I am starting to think that there is some kind of threshold involved and that the more apps and data stored on the Fusion Drive, the slower the boot time gets. But that's just guessing.

For now, I'm going to keep it this way, putting my iMac to sleep instead of shutting it down every evening. Wake-up is instantaneous and everything is super fast and responsive. One day, with enough time on my hands, I will wipe my system once again, clean install Big Sur, and install all apps from scratch, one by one. I need to prepare this thoroughly and have to record a lot of settings. There's some fifteen years of creative work stored on this machine, and it's really fine-tuned to the limit.

I think your conclusions are correct: earlier versions of Big Sur had a problem where system files were incorrectly replaced by application files on the SSD, or some other SSD issue emerged causing the performance issues. On 11.3 I now have Office, Xcode, iWorks and some other apps installed with no performance degradations: a few seconds were added to the boot process and that's about it. I installed 11.3.1 yesterday and was quite nervous about it, thinking it would mess up my system again. I took very long to install (with at least 5-6 reboots) but performance stayed on par. I'm now quite confident the issues are fixed for good.

This new information has encouraged me to upgrade from Mojave to Big Sur on my 2017 27-inch iMac. Thank you, Tomeranary and Deep Sky Diver, for sharing your experiences, good and bad, and keeping us informed of your progress. Stay safe and well.

I've given up on Big Sur until there's absolute certainty that a new release addresses Fusion Drive issues.

I've wasted weeks of my life dealing with this. Things would slowly devolve to being spinning balls waiting on anything to happen, lag on clicking on items in Finder or Apps, slow bus speeds of copying files, long boot times, and finder/files taking even longer to show up.

I've done many of the aforementioned processes. Reinstalled Big Sur over the existing, and it would work better for a bit, but then back to issues a day or two later.

While I had a backup of my computer already, I was concerned about a couple things (including a VMWare Virtual Machine) that may not have been backed up fully or as recent as I needed it. The ability to backup from this troubled Fusion drive to a USB, a WebDav, or a Thunderbolt Target Drive to another Mac was moving at a snails pace... it would have copied a few gigs in days!

I finally decided to just format the hard drive/resetFusion, and install Big Sur 11.3 clean from an external drive. Did not install many apps for a few days, and just used it. Let it sit on Desktop several times and reboot like it's been suggested too. Install a couple nominal apps and moved files from backup (not any system/library files at all). It all came right back eventually.

What is obvious is that something in Big Sur is affecting the Fusion partitions such that even acting as a Target Drive (not running OS, but simply a connected drive), is a problem to use it. Combinations of Safe Mode, Recovery mode, reinstall OS over existing, will at least make it usable for a while so you can pull files off it.

I formatted again, clean installed Catalina, including all my files and apps. I have NONE of these issues with Catalina. Days now... quick boot, no spinners, all is good.

I can't keep wasting my time on this and will stick with Catalina until I learn something new about a release that Apple acknowledges.

iMac (Retina 5K, 27-inch, 2017)

3.8 GHz Quad-Core Intel Core i5

40 GB Ram

Radeon Pro 580 8 GB

1TB Fusion

I've been following very closely on the issues arising after people with fusion drives upgrade to Big Sur and have been putting it off, and still am on Catalina. Do you guys recommend to do it now or wait for future Big Sur updates? If you recommend upgrading now or in the future, what is the approach and appropriate steps I should take?

While I did suffer from the issues mentioned here, I do recommend updating to get the latest features and security patches. I assume the performance issues are not that widespread so your chances are pretty good (I do not have any data on that but imagine that the issue would be more prevalent in the media if every single fusion drive was affected).

I only had my issues fixed after doing a clean install (including running resetFusion) of version 11.3 but the poster above had no such luck so it’s not a guarantee.

Well, let's say that that my iMac (21" 4K late 2015) went from "always very nice" to a "total royal pain" in the space of only 4 months. Nothing new installed except Big Sur.

I do have the 2TB + 128 Gbb and it's mostly used by my wife to run office, spotify and browsing our photo library from time to time.

The computer is fairly old for "my" standards (I'm an IT professional) but this rapid deterioration is unheard off for an Apple device... are we back to "Vista upgrade experience" again?

No, it does not. Some users report faster boot times (around 1m10s - 1m30s), but others, like me, see no improvement and have to deal with a 1-year old iMac crawling during 4 minutes or more until Finder or any app becomes responsive. It seems to me that the amount of space taken up by apps and data on the Fusion Drive, and the fact that Fusion Drives are by their very nature prone to defragmentation, both play a role in this. My 1TB Fusion Drive has more than 500GB of free space on it. It also seems that doing a clean install can - in some cases - either solve the problem or improve the boot times from 4min to 1 or 2min.

I had my problems fixed by a clean install of 11.3. (Before it took 4min to boot)

At the end of the upgrade process to 11.4, a message came my system would be optimised for performance. It took a fair while (reorganising files?) and boot times improved from 30s to 20s.

I'm considering performing a clean install as well. But when I did that with 11.1, it didn't make any difference at all. The problem is that for my work I have photo and video software that is fine-tuned and has a number of plug-ins that need to be fine-tuned as well. Basically, doing a clean install takes me 2 days before everything is up and running again. I can't afford to loose so much time if I'm not 100% sure it will definitely solve the problem of such slow boot times.

VikingOSX: Yours is the most useless response I have ever seen in a forum. Should I have "bought" or hired an entire engineering department to fix my iMac 27?

But regardless, where is the solution to the slow startup with BigSur? Seven months later it still still very slow.

And not, it is is not only a startup application. I have no applications set up to start when I turn my computer on and still, not only the computer itself takes up to 10 min to start. Opening web browsers, Microsoft applications or (gulp!) Adobe apps takes such a long time that I have programmed myself to do other activities while everything is finally set up.

Alas, the buttons do not include a Not Helpful choice.

neerajlaw,

Please read the Terms of Use you agreed to, you can read them at Terms of Use

PS. In yourt case, I would recommend asking for assistance - just in case things get hairy.

Some extra info:

https://support.apple.com/en-us/HT207584

About fixing fusion drive.