Very slow boot on Fusion and Big Sur

I tried reinstalling everything from scratch, as you described, and also creating a new user, in order to reset the profile, but nothing works. My boot time with Fusion Drive is about 1 minute 25 seconds. Probably the 24GB on SSD available on my 1 TB Fusion Drive are not enough for the Big Sur requirments (they were for Catalina). I solved booting from an external SSD on a USB 3.0 enclosure. Now it boots in 35 seconds and everything is very fast.

Download and run Etrecheck. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support  to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

and use the Additional Text button to include the report in your reply.

IMPORTANT:

Before running Etrecheck assign Full Disk Access to Etrecheck in the Etrecheck's Privacy preference pane so that it can get additional information from the Console and log files for the report:

Also click and read the About info to further permit full disk access.

Then we can examine the report and see if we can determine what might be causing the problem.

I think a clean install would help you out. The 128 GB SSD blade of your 1TB Fusion Drive is more than enough to accommodate the OS and its essential apps. My guess is that an upgrade installation of Big Sur over a previously installed OS is not always able to recognise or use the SSD blade as it should. Other users who have a 128 GB SSD, have been successful in making Big Sur load in less than half a minute, after a clean install, not an upgrade install.

QUOTE FROM ANOTHER THREAD:

“Restart in Safe Mode - Shift _key immediately at startup. Will do a Repair Disk, clean cache files and only loaded required software to boot computer. It will take longer than normal to boot - Normal. Once logged in it will appear different than normal - Normal. Let it run this way for 5 - 8 minutes and then restart in Normal Mode... ” P. Phillips User Level 6

-> Don’t know if that particular advice from P. Phillips at Apple Support Communities actually worked or not in my case, but my Big Sour now loads MUCH faster!

Boot time with Catalina used to be almost immediate (10-15 sec), but with BS 11.2.0 and 11.2.1 ended up at an excruciating 50-60 sec. So just before upgrading to 11.2.2 earlier this week, I did as suggested above i.e. a proper ‘Safe Mode’ startup (waited 20min, so as to let the system do its cleaning job), then restarted normally - still sluggish - but right after that, I finally installed the 11.2.2 update. Now it flies: 12-15 sec. max!(?) Big Sur not Big Sour anymore ; )

Was this the beneficial effect of a deep cleanup operation as a first step, or simply an improvement implemented by Apple via its 11.2.2 installation process? Oh, and how should I approach the newest 11.2.3 version that came out 72hrs afterwards!? A bit scary ; (

(Note: my iMac is a late-2015 model with a 2.128 TB Fusion drive, so ‘Big Sour’ sluggish startup is surely not only affecting smaller fusion drives with a 24 or 32 GB SSD blade...)

There are a number of users that own your type of iMac with the 2 TB Fusion Drive featuring the 128 GB SSD blade and have been able to make Big Sur start up in a normal way and have all apps running fine, after a clean install. Even on my 2019 iMac 1 TB featuring a 32 GB SSD blade, I have been able to make Big Sur start up in less than 30 seconds, but only after a clean install and before installing any apps (e.g. Pages, Numbers, Keynote, iMovie, Garageband). As soon as I added those Apple apps, the startup times went crazy (first over 2 minutes, and finally over 4 minutes), so I didn't even try to install 3rd party apps (e.g. Adobe Photoshop and Lightroom), and downgraded back to Catalina, which made my iMac very, very happy. Big Sur appears to have a problem with the amount of available space on the SSD blade and positioning itself and/or apps on that SSD part of the Fusion Drive or on the HDD part, during and after startup.

After updating from Catalina to BigSur I experienced the issue and I re-installed BigSur from scratch (and also the all the applications). The results were not good at that time, then I started booting from external SSD drive, forgetting the Fusion Drive. Some weeks ago I started trying again and I found that booting the system several times and allowing it to run for 20 - 30 minutes without using it, improved the booting time as documented before (52 seconds from the password typed to the desktop rendered).

Today I installed the 11.3 in the following way: I downloaded BigSur on another Mac. Then I created an install media on an external SSD. The I booted from the external SSD and I asked to install the new Big Sur 11.3 to the Mac HD. After the installation I let the system idle for one hour. Then I rebooted, it obtaining the new results (19 seconds from the password to the desktop). It's the first time I install Mac Os in that way: all the other times I followed the standard way. I don't know if the success is because the 11.3 has changed something or because installing from the external SSD the system the OS is installed directly in the SSD portion of the Fusion Drive.

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.

Let's use some logic to see who is correct and who is not.

1. There are iMacs out there that have SSD blades of 24GB, there are others (like mine) that have 28GB, and some that have 32 or even 128GB of SSD "fastness" in the 1 or 2 TB Fusion Drive "miracle".
2. For those of us who have anything less than a 32GB SSD blade, upgrading (from Catalina), installing from scratch, or re-installing does not change anything to the unacceptably looooooooooooooooong boot times of up to 3 minutes and more! A PC from the late 1980s loading Windows 3.1 did better...
3. If we go to Disk Utility and check how much space is being eaten up by some kind of disk image that is now being used as a restore point or upgrade point or whatever, on the SSD blade of the Fusion Drive, it says more than 15GB (!). The installer package of Big Sur alone is over 12 GB, meaning that once the OS in fully installed, it will be even bigger.
4. So, third-party apps and caches and frequently used chunks of data (like photo or video or music libraries) that the OS would like to load on SSD blades of anything less than 32GB, make it impossible to have the OS reside permanently on that same SSD blade. Therefore, it is residing on the much slower part of the Fusion Drive: the HDD...
5. When I start my not-even-one-year-old iMac 2019 5K 1TB Fusion Drive with 40 GB of RAM, it takes 3 (three!) minutes before I can start any app. That's how long it takes to boot, to login, to load the desktop and the Finder, and some items on the desktop. During those full three minutes I hear the HDD work very hard, which proves that I am right about the OS residing on the HDD, whilst it should be on the SSD. During boot, login, etc the system is copying the whole OS from the HDD to the SSD, and only after I have started up a number of apps, it starts looking at what apps and data should be copied from the HDD onto the SSD.

So, no... Big Sur does not have "plenty of space" on a 24 or 28 GB SSD blade. And it could be that when more apps are being installed, even a 32GB one would be insufficient.

THAT, in my humble expertise of 35 years in hardware and software, is a DESIGN FLAW of the OS. Catalina started up on my system in 30 seconds or so. I would understand that a bigger Big Sur (what's in a name...?) would add ten seconds or so, but 2 and a half minutes???!!!

No, there aren't any launch daemons or launch agents or login items or hardware causing this. It is the OS. And it is FLAWED.

And, finally, to say that the solution (!) for Fusion Drive iMacs that are as good as new, is to add an external SSD to boot from in a reasonable amount of time, is like saying that to start a car's engine, you need a couple of people pushing it. I'd call that "solution" an expensive and cumbersome work-around, and totally unworthy of the inheritance of Steve Jobs.

Apropos, my posts dated (1:23 AM & 2:55 AM); I had only two options either to go in for a new Mac or for replacement of 'Fusion Drive' with 'SSD' as was suggested by one of my friend, to whom I used to regard as a true wizard (before this fiasco).

However, the second option did not found favour with our find here 'Deep Sky Diver' so I looked for help from apple support, who willingly extended all the help they could on two occasion, but all of it proved to be of no avail.

Hence, before taking the big leap, I decided to gamble on SSD (although even apple people were also skeptical about its efficacy) and EUREKA!!!!!! Upgraded system from High Sierra to Big Sur ; restored my files from time machine ; and now my Mac is starting up in just about 25 seconds. Yuppie!!

So mu sincere advise, if at all you want to do anything to salvage this grim situation today itself, you do not even have to wait, just get the SSD in place of 'Fusion drive' and that is it. 'Good Luck' to you all

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.

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]

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.

Hi!

I may be able to give you some pointers.

Let's try:

1. Booting into safemode; https://support.apple.com/en-us/HT201262
2. let's delete (minus sign) login items: apple menu > system preferences > Users & Groups
3. Let's open Finder and go to menu, Go > Go to folder > ~/Library/Caches >>> select all (CMD + a) > new folder with selection, do the same for "Saved Application State" and reboot.
4. Still trouble? Let's create a back up and contact AppleCare!

Hope this helps,

Met vriendelijke groet / Best regards, Wempe

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).