Very slow boot on Fusion and Big Sur

Thanks for posting this and I am so glad I found your reply. I was driving nuts when my iMac slowed with the boot. But I noticed some apps are also slowed down like Lightroom. I have a 2017 4k 21.5 3.4Gh iMac with 1TB Fusion drive and I started to worry about all this. I guess it's all about BigSur. I guess the only solution is to wait for the upgrade or get sad inside.

It gets worse. I turned my iMac off for the weekend, and booting this morning took 12 minutes (!) before I got a responsive desktop. Even the Music app bounced for 2 minutes...

Then I got 10 push notifications stating an error with installing apps. It were iOS apps I installed on my iPhone. Obviously they can't run on my Intel iMac. What gives? Apple needs to step up its game with this macOS release. Fast.

This is the first time I am not updating all my Macs to the latest version.

Well, iMac 2017 2Tb and 128SSD -- and guess what, I am here looking for help. Same ridiculous update and start up times. Applications are unresponsive and I was too late for a meetings few times already. Have to run it 24x7 now. Have 40 GBs of RAM installed, that is the only solution to use it without pain after startup wait times. Considering to sell it for all the good and bad it has. Do not think Apple is interested in our complains. They are selling M1 computers now...

Mine is {iMac -2017 with Quad-core Intel Core i5 processor (3.4 Ghz.) L2 Cache per core) RAM – 8 GB} Fusion Drive – 1 TB). Earlier the machine was blazing on High Sierra – start-up time about 20 seconds.

During some weak moments, succumbed for upgrade due to constant pestering messages from Microsoft office 365 (updates available but you need to upgrade OS)

Thereafter, the quest began, scrambling to regain what I lost due to my own imprudence.

Apple service centre guy recommended the first step {Upgrade the RAM from meagre 8 to 32} promptly done spent fortune with no results whatsoever.

Second recommendation (delayed due to festive season) Replace 1 TB Fusion Drive by 1TB SSD Drive.

AND nothing works then you may do you tiny bit of contribution in overflowing Trillins dollar company by buying new machine (beg, borrow or steal) since that was the intent right from beginning ; under the garb of developing new software and removing non-existent bugs and glitches.

As ay other reasonable sane man, I also requested the tech guy, to relegate my machine to Catalina or High Sierra (10.13.6) {which was doing very good job). It took him two hours to do just that because apple had locked the ‘Fusion drive’ in the process of upgradation of Big Sur. He had cross several hurdles before he could bring it back with a bootable drive of Sierra and used My “Time-Machine SSD”.

AlAS! Even now the start-up (in sierra – with my old files and setup) is procrastinating and it has become a harrowing experience watching it coming to life. 

I have gone through all the suggestions given above thread, and as is apparent, none worked. Even the outside SSD has not worked eventually.

To quote from ‘Deep sea Diver’ “Those of us who have small SSD blades as part of the Fusion Drive system, will indeed see bootup times of in between 4 to 5 minutes”… If I have understood it correctly, the suggestion of Apple service Centre guy (replace Fusion By SSD) should work.

Need your expert opinion of this, before I embark upon this expedition..

Thanks in advance.

Thanks for this prompt response and for your words of wisdom Sir. I am in complete agreement with what you state in para 3. But in So far as parts 2, probably I did not male myself clear. Apple people would remove original ‘1-TB Fusion drive’ & install ‘1-TB SSD’ in its place.

So, should I hope, it will solve the problem.

I am going to wait a bit longer and hope Big Sur gets fixed with a future update. I can't go back to Apple Support with my 2015 as it would only cost me money. BTW: I have 24Gb of RAM, needless to say it doesn't make a difference. I do understand Big Sur is more taxing on the system, but this performance drop is of a different magnitude.

I'm not quite sure what to make from your system still running slow on previous macOS versions. Maybe a clean install will fix the issue?

I have the same problem iMac 2019 with 1TB Fusion. I've followed the comments about removing Avast etc and followed the Apple Support advice which included reinstalling Big Sur but has made no difference to the start up times. I just hope they fix this in 11.2.4.

Firstly,

In Disk Utility, there is only one SSD.

Secondly, the original 'Fusion Drive' was removed in my presence,

And

Lastly, the original apple's drive is now doing duty as 'External Time Machine' having been safely installed in an external HDD enclosure of 'Transcend'.

[Edited by Moderator]

Thank you very much, Fabio_V, for sharing this information. I think what you say about the executables makes sense.

I have a few questions for you. Would you be so kind as to answer them?

1. How did you install Big Sur to achieve this more reasonable boot time (upgrade from Catalina? clean install?)
2. What version of Big Sur are you on (11.2.3)?
3. You say "52 seconds from login screen". I suppose you mean "52 seconds from startup chime to login screen" or am I missing something?
4. How many seconds does it take, after login, to reach a responsive desktop and responsive applications?
5. Do you have Apple apps such as iMovie, Pages, Numbers, Keynote installed?

Resolved... for you perhaps, but not for many of us who have followed that procedure already months ago without any difference in startup times between 3 to 4 minutes before any app becomes responsive.

Unfortunately I don't notice any major differences:

• boot to login screen: 1min
• login screen to desktop: 2min10 (with OneDrive launching automatically)
• Launching Outlook: 1min 40 (54 icon bounces!!!)
• Launching Safari: 50s
• Launching Mail: 45s

maybe I need to give it more time. We're only the end of April... ;-)

Dear Fabio,

Thank you, once again, for this very useful and positive news. Can I ask you, also once again, for a favour. Many of us would like to give it another go, but cannot waste anymore time in case the result would be negative and we would have to downgrade back to Catalina. So, please, could you detail, step by step, how you managed to get to this result? I asked you before for some more details, but there are more questions remaining and it seems it's very important for us to be able to copy exactly every step of the way.

I know you did a clean install and allowed Big Sur to do its work for 20 to 30 minutes after that install, without starting any application. But what I would like to know also is how you actually restored all your apps and your data. Two of my main questions are: Did you, at the end of the installation procedure make a new account in Big Sur without restoring anything at first, or did you simply follow the instructions of the Setup Assistant and immediately copied over your apps, data, and settings from your Catalina account? Second question: What method did you use to restore your apps, data, and settings (a Time Machine backup, a clone from your Fusion Drive made by a third-party application...)?

Again, it would be so useful for so many of us if you could detail, step by step, numbering each step, how you got Big Sur booting normally and running normally on your iMac with 1 TB Fusion Drive with a mere 24 GB on the SSD blade, from installing Big Sur to using it right now. Thank you very much in advance!

OK, I understood better now. I will try to summarise the steps you took, from the moment you installed the previous version of Big Sur some time ago with no improvement of boot times, up until today's version 11.3, which you installed over the previous one, using an external SSD, preserving the account(s), apps, and data.

1. Clean install of Big Sur (a version from before 11.3).
2. Manually re-install of apps and data.
3. Partial improvement of boot times, apparently because of allowing the system to be idle for 30 minutes or more after installation.
4. Today's installation of Big Sur 11.3 was done from an external bootable drive with the new version on it (macOS Big Sur Installer), not reinstalling from scratch but simply overwriting the previous version of Big Sur and thus preserving apps and data.
5. Boot times are now down to what can be considered normal (under one minute or less).

Am I correct in what I wrote above? And have you restarted your iMac a couple of times since you installed 11.3 earlier today?

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.