Very slow boot on Fusion and Big Sur

Today I just updated to 11.3, I did not reinstalled the system. I did it as described in my previous post (booting from an install media I prepared on a external SSD). Please notice that this installation preserves you Data partition.

Yes, you're correct.

In addition to your step #3: after installing huge applications, please boot the system 2 -3 times, letting it idle for 30 minutes. As far as I understand, the magic of the Fusion Drive requires the system to be able to re-arrange data. I think this will continue to be valid in the future.

Now the boot time is 10 seconds with the Apple until the login prompt and then 19 seconds to the desktop. Filevault is on.

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.

Dear Fabio,

Thank you, very informative!

If ever you install another large app like this or copy a number of large files, and then let the system be "idle" for 30 minutes or more, could you please first open Activity Monitor and check under the "CPU" tab which process(es) are using the CPU most (I suppose you know how to do that, to arrange the processes according to the percentage they are using, from most to nothing?). This could reveal what the OS is doing during the 30 or 40 minutes of "idle" time. This process or processes should be the one(s) that manage how apps and data and system files are arranged on the Fusion Drive.

When looking in Activity Monitor, the only processes that seems to generate a lot of disk activity are kernel_task, launchd and mds_stores (related to Spotlight). I also now notice that Memory pressure is way low: no apps or processes go higher than 250MB RAM. Before reinstalling Big Sur (when my system was extremely slow) I noticed processes easily going over 1GB. Unfortunately, I can't remember which ones.

While playing with my now fast iMac, I notice that every app I previously opened and quit, now opens within seconds, including big apps like Outlook. It did not do that before. I have 24GB of RAM, plenty of storage to keep apps actively in memory, but that was clearly also something that was broken before.

I was also wondering: are you all using the new APFS file system in combination with the Fusion Drive? It creates two volumes, a (non-writable) system volume and data volume. I would assume the system volume is on the SSD, but maybe that's not a given?

You could definitely be right. I'll be downgrading to Catalina, worked snappy. It's sad to downgrade but it's the sensible thing to do until I'll upgrade my iMac this fall.

Well, many times it is the user's fault as they would install various "cleaning" and anti-virus apps which when removed removed the problem.

I'm experiencing the same issue and I agree. I reinstalled Big Sur twice without any improvement. After few reboots the boot time decreases, but it remains far higher than on Catalina. In addition, when writing a significant amount of data, the boot time increases again, probably because the boot files are removed from the SSD. Maybe Apple should find a way to keep "locked" into the SSD the most relevant system files and apps, in order to allow for a smooth processing.

Careful if you let "Big Apple" know about "Big Sur" not being able to boot a one-year-old high-quality and very expensive iMac in less than 3,5 to 4 minutes... I already let them know 3 times since mid-November, and 3 months and 3 versions later still no fix, no acknowledgment of the existence of the problem, and if you dare to say anything else but purely "technical" stuff, you risk being censored or worse...

Apple is wonderful. Big Sur is great. And everything works perfectly... But I don't believe that anymore. The problem lies in the simple fact that Big Sur is too big to fit on a tiny SSD blade together with the most essential apps out there.

The feedback page is: https://www.apple.com/feedback/macos.html

I have a late 2014 Imac 5k with Fusion Drive. That particular old Fusion Drive has 128 GB of space - and the issue is the same. A LOT slower boot time than previous generations of MacOS. Furthermore, the drive is spinning audible under load constantly - that was not the case before.

I don't expect SSD-loading times. But I also don't expect new iterations of MacOS not support the Fusion Drive properly.

And that seems to be the case.

In my case, a late-2015 2TB Fusion iMac, Catalina (and all previous OS) would always load in a lean 12 seconds; BS 11.0, 11.1, 11.2, and 11.2.1 would all of a sudden load in a minute i.e. 5x longer; earlier this week I was excited because the freshly installed 11.2.2 had brought back its startup time to an encouraging 15 seconds, thinking that perhaps Apple had cleaned its mess... Now, BS 11.2.3 puzzles me with its lukewarm 30 second boot. Why so much discrepancy between OS versions on the same system, and between different Mac users? 5+ minutes is actually 10x longer than before, unbelievable! Let's hope that 11.2.4 comes with a solution as soon as possible.

Thank you, Fabio.

Several months ago, I also was able to get a proper boot time installing Big Sur from scratch (clean install). However, as soon as I started installing apps like Pages, Numbers, Keynote, and iMovie, the boot time went up again to almost two minutes. It seemed to me that, adding apps and/or data to the Fusion Drive, made Big Sur move essential parts of the boot system to the HDD part of the Fusion Drive. I never had any slowdowns once Big Sur had taken the time to boot and to load the OS and the desktop. After about four minutes every app started up and worked fine. But the boot times stayed the same, in between 3 and 4 minutes.

So, until now, to me that is nothing new, that installing Big Sur from scratch allows it to boot in about forty seconds or so, from Apple icon to desktop.

However, several important questions remain in order to be able what is the right procedure to follow to achieve normal boot times:

1. If I understand you well, today, you installed the update of 11.3 over an existing Big Sur version (11.2.x)? Or did you, once again, do a clean install from scratch and then re-installed all your apps and restored your data?
2. How did you restore your original account if you did a clean install today? Using Setup Assistant or did you create a new account?
3. In case you used Setup Assistant, did you restore everything from a Time Machine Backup or from another backup or clone?
4. In case you created a new account, did you re-install everything manually (basically moving the apps and data from your previous account to a new account)?

Again, to make myself clear, I once also managed to get Big Sur boot in a normal time frame, but only before re-installing my apps from scratch. So it's very important to know as clearly as possible how you restored your apps and data in case you re-installed Big Sur 11.3 again from scratch.

Whether the positive result you are having now, is due to the new 11.3 version or to the fact that you left the system idle for one hour, we cannot know at this moment. But it's very important to me and many of us to know exactly how you re-installed your apps today, or if you simply installed 11.3 over an existing Big Sur system that was booting extremely slowly until now.

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.

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.