Very slow boot on Fusion and Big Sur

Thank you very much for all the information. I'm tempted to give it another try as soon as my work schedule allows it, by trying to simply do an upgrade directly from Catalina to Big Sur 11.3, booting my system from an external macOS Installer drive, and then simply overwriting Catalina with Big Sur, leaving my accounts, apps, and data as they are now. That would be the fastest and easiest way for me, although your procedure was different as you updated today from a previous Big Sur installation. If it works out fine, I will give feedback here and on another thread, but it could take a few days or even longer before I have the time to do this. As you recommended, I will allow the system to be idle for about an hour before starting up any applications or rebooting. But if we need to do this every time a large application is installed or updated, it would be a big nuisance.

I'm not sure that upgrading directly from Catalina to Big Sur using my method is a good idea. May I suggest to upgrade using the standard way ? Anyway, if the results are not good, you can run the installation again using my method. It simply reinstalls the full system into the system volume, preserving the data volume and can be used also to fix a non-booting system.

I had the same problems with my iMac after installing Big Sur: Booting took forever and everything disk related seemed to be quite slow in general.

Installed the update to 11.3 on the usual way and got a notification about my Mac being optimized after booting for the first time after the update. And now the problem seems to be gone: Back to Catalina speed while booting and while using the Mac.

I've been struggling with this for days now.. and of course weeks prior with it getting slower and slower and not knowing what was going on. This now makes sense for my fusion drive mac.

One quick question as I test some of these ideas. When you guys have said to let boot and site idle for 30 minutes (or even an hour), then reboot and do again 2-3 times.... are we talking about letting it boot and sit at the user login screen for 30min+ then reboot? Or login your user and THEN let sit for 30+ min on the desktop and then reboot?

thanks

Can you please stop spamming these boards with advertisements for Etrecheck? It’s getting a bit much. With regards to this issue, nothing relevant has come out of it.

As far as upgrading to 11.3 goes:

I did a normal in-system update.

as posted above, after reboot I did see the new “optimising your Mac” notification

boot times have not improved. Boot to login screen: 1min, login screen to desktop: 2min10

I left the system idle overnight so it had plenty of time to reorganise files

The next morning I rebooted. Boot to login screen: 45s, login screen to desktop: 3min20 (!)

So it was even worse. Interestingly, I set the screensaver to kick in after 2 minutes. And yes: it started and played smoothly. When I moved the mouse, it kicked back to an unresponsive desktop (that was still not complete and beachballing).

if I find the time, I will reinstall the system from external media and see if that improves anything, but I can’t imagine it will.

No one from this thread has ever uploaded an EtreCheck report. No one is giving it a chance to help. I agree that EtreCheck is the next step to do here, as it can find potential issues as to why boot times are slow.

Cheers,

Jack

I tried it (I guess in another thread, this board is full of Etrecheck posts) and nothing useful has come out of it. But if you feel it could be useful, definitely try it and post back. It’s a commercial tool that requires you to pay for a full list of recommendations, but the basic version should suffice.

EtreCheck has not discovered anything wrong with my iMac nor with anyone else's having trouble with 3 to 4 minute boot times on Big Sur. We have posted the reports on other threads months ago. In the mean time, No suspicious software, no suspicious login items, no suspicious launch agents nor daemons. Apple engineers have acknowledged there is a problem with Big Sur and Fusion Drive systems. Big Sur 11.3 seems to have solved that problem for some who have installed it from an external drive, after booting from that same external drive. This makes sense and is totally in line with what several of us have logically concluded, i.e. that the root of the problem lies in how Big Sur is able or not to put what part of the OS on what part of the Fusion Drive (HDD or SSD blade) at what moment of the boot procedure and when running the system.

As suggested above, I just tried to reinstall Big Sur 11.3 from an external drive on my iMac. The good news is that this definitely makes a huge impact on performance.

Boot to login: 1 min --> 40s

Login to Desktop: 3 min 20s --> 1 min 50

Launching Outlook: 1 min 40s --> 20s

Not exactly great numbers (and not quite normal yet) but definitely a huge improvement. Also, my system feels much more snappy and responsive. It's quite an easy process as you don't need to reinstall or reconfigure software, so it's definitely something you can easily try.

If you're not very technical, you can follow this guide: ***

[Link Edited by Moderator]

Have you previously installed or run any "cleaning", "optimizing", "speed-up" or anti-virus apps on your Mac?

And no, I won't stop asking people who come here for help to use Etrecheck to aid us in diagnosing the situation. It's the best tool we have to get to the root of the problem.

No, we don't have any cleaning, optimising and speed-up tools running. We even have this issue with clean installs of macOS on our devices. Etrecheck did not reveal anything, Apple has acknowledged the bug in Big Sur.

The reason why I'm annoyed with these Etrecheck posts is that some of the guys pushing it are giving wrong advice and claim it's all our fault because we have installed some software and that Big Sur is not the issue because other people don't have downgraded performance. I don't like these blame games.

Encouraged by the good results of reinstalling Big Sur 11.3 over my existing installation via an external drive, I decided to bite the bullet and do a complete clean install of 11.3:

The results are simply amazing:

Boot to login: 1min —> 20s

Login to desktop: 3min 20s —> 10s

Launching Outlook: 1 min 40s --> 20s

Launching stock apps like Finder, Safari and the App Store are nearly instantaneous, within one bounce.

Note that I did a clean install before with version 11.1 and that did not make any improvements. But now with version 11.3 it clearly has. I will now leave my machine overnight and check back tomorrow if things keep humming along.

For those interested, this is what I did:

- backed up my data and documents

- reboot in Recovery Mode (Command+R) and erase all internal partitions / volumes  with Disk Utility

- launch Terminal (from Utilities menu) and use the “diskutil resetFusion” command to rebuild my Fusion Disk

- install macOS Big Sur (it took a very long time)

- did not restore any Time Machine backups

- login and gave it some time to download iCloud stuff

- rebooted to verify performance

- installed some small productivity apps like Things, Agenda, Paste, …

- waited for Spotlight indexing to finish

- rebooted to verify performance

- connected my external USB disk and speakers

- waited for Spotlight indexing to finish

- rebooted to verify performance

- installed MS Office without launching it (it took a very long time)

- rebooted to verify performance

- launched and configured MS Office and OneDrive

- rebooted to verify performance

So far, I'm still at a responsive desktop in 30s (down from 4min20s). Fingers crossed.

For me it's crystal clear now that everything related to disk read/writes are the main issue (before reinstalling). For instance, I kept some files on the Desktop (no more than 15) and that was the part where the boot up process took over a minute to get those files to show up (even the thumbnail in the Download stack in the Dock remained blank for a minute), launching Finder windows took forever, copying/moving small files took way too long, etc. I guess that's also the reason why booting and launching apps was so slow.

And now, after reinstalling from scratch, it's all instantaneous. I kept my iMac on overnight, and performance is still the same. So Big Sur hasn't started reorganising files on/off the SSD blade of the Fusion Drive. All stock apps open instantaneous. My biggest apps (Office) are clearly on the slow hard disk part, but they still launch within 9-17 seconds, which is perfectly acceptable for these big apps on an old machine. Adding OneDrive and Paste as items that launch at startup only added a few seconds, the way it should be.

To reply to your questions:

1) I did not: I terms of big apps I had MS Office, iWorks, Pixelmator Pro and Xcode.

2) I only reinstalled MS Office so far (but these apps are also approaching 5GB)

3) My Music and Photos libraries are huge (200GB) but I keep them in the cloud with the options to "Optimise Mac Storage" enabled.

4) It's a 1TB with 24Gb SSD blade: it still has 960GB free (as most things are still in the cloud now, even OneDrive does not sync anything I haven't used yet). So I'm well over my SDD capacity.

The big question remains: when I install more apps and download more data, will Big Sur all of a sudden swap crucial OS files away from the SSD part or not. Only time will tell.

From my experiment I can almost certainly conclude that reinstalling from scratch is the only (possible) solution (if something did in fact change in the way 11.3 operates, which we still not know for 100% sure). Restoring your apps and data from a Time Machine backup could potentially be fine as well as the important thing is that the OS is kept on the SSD blade, but I'm not going to try that scenario ;-)

Thanks for the info!

Whatever the cause of the problem, it's definitely a complex issue. And it's important to consider that, although most of the users with this problem of incredibly slow boot times, have a Fusion Drive iMac (from 2015 all the way up to the 2019 model), we are using different apps and have different amounts of data on the Fusion Drive and/or in the iCloud.

Your 1TB Fusion Drive is pretty much "empty" compared to mine (I have over 470 GB free), so that could definitely be a big help to Big Sur on your iMac.

So far, both you and Fabio_V, seem not to have installed any larger third-party apps like Photoshop or Lightroom Classic. Yet, like I said above, a few months ago, installing 11.1 from scratch, allowed me to have a boot time of 20 seconds into the desktop. But at that moment, my account was new (no migration yet) and virtually empty. Installing Pages, Numbers, Keynote, and iMovie instantly made the boot time two or three times as long... Re-installing Photoshop and Lightroom, and connecting to the iCloud made the boot times go up to three minutes again. However, once everything had found its proper place, launching every single app and using it was very fast.

And yes, in your case, only time will tell what will happen once you add more data or more apps.

Whatever it is, there seems to be some kind of threshold of data being swapped around between the HDD and SSD parts of our Fusion Drives that defines if Big Sur is able to start up in a reasonable amount of time or not, and the "logic" of the software behind that apparently cannot be adjusted or managed easily or correctly by Big Sur.

You're right. Note that I also did a clean install with 11.1 and while I did notice a performance improvement over the installation where I upgraded from Catalina, I never had the performance boost I'm seeing now with a clean 11.3. Not even close.

Obviously my Fusion Drive is now nearly empty as I completely erased it and even rebuild the containers/volumes using the resetFusion terminal command. It will now start to fill up when downloading files from OneDrive and iCloud. I will now also install iWorks, Xcode and Pixelmator, so those are large apps as well...

I'll report back if I notice sudden drop in performance.