iMac slows down after Big Sur installing

I have late 2015 iMac with 16 go ram and my computer becomes useless. Boot time is about 45 minutes. Before that, nothing responses properly. My computer became a junk. Worst update ever.

iMac, 2017, 8gb ram
Same here - won't open programs, slow, shuts down to login screen. The computer worked completely fine before the Big Sur update. Please fixxxxx.

MacBook Air (Retina, 13-inch, 2020)

Big sur was a big step down in my macbook performance. Has been a pain in the *ss working with my laptop since I updated the OS. The fan works all the time, and there is a serious lagging with the apps.

time for a look at causes a bit.

Lots of complaints. No answers.
this is a Dev to Dev forum. I doubt Apple has much interest in our complaints here.

I’ve narrowed this down a bit. I do a lot of large scale file movement. Be it transferring drive to drive or renaming batches, in the hundreds or thousands of files at a time. opening and modifying multi-gigabyte documents (PDF et al). Other enormous file system tasks (compression, decompression etc).

there is something wrong with the file system handling. It’s that simple.

maybe some other users with different setups can help me track this down?

2017 27” iMac core 5.
64gig ram available.
256GB main drive.
22 external drives. Range 512GB-8TB. All but one are SSDs.
all drives APFS
All non-system data is on external disk.

booting with my externals off Takes about 20-30 seconds. Not bad. Booting with them turned on is understandably slow and that’s always been an issue. So I’ll focus on post boot.

finder has no issues with the onboard disk. Probably because I’ve done nothing to it mod wise and don’t store any external data on it. I Symd documents to an external.
some of my more full but lesser quantity disks have no issue either.
loading up a folder with a few thousand files in it sparks a spinner. :(

regardless of the number of files attempting a batch rename causes major delays and occasionally crashes. I’ve had it as minor as the app crashing to finder restarting to a whole system crash.
(I use ReBamer and NameChanger mainly but also A->B and the cl tool rn.)

ingesting more than 100-150 files causes a freeze. System may or may not overcome it.
Actually changing more than a handful of file names also crashes.
finally in batch transactions such as a replace action, (eg rn . = [space] or rn _ = -) it locks up after about 50 reads, regardless of number of changes.

file count heavy actions such as loading Acrobat CC and a portfolio causes a hang.

looking through multiple threads about the slowdown and my own experiences, most lead me to believe this is a file system issue.

slow boot on a single drive or a hang on a 1500 file directory equate to the same thing given other similar freezes.

did apple change APFS with the pre-R beta to the post-r betas?
I’ce tried rebuilding spotlight and repairing file maps. Both fix issues for a brief time; a few minutes to a few hours.
I’ve also tried dual booting a clean BS 1b2. Boots and runs fine. Until I access an external drive. Then the same freezes.
my drives are fine. According to MacOS, SMART, and manufacture tools when testing them through a live boot, not on my iMac and on a laptop.
my RAM is fine. So says a live boot of MemTest.

that leaves the software being the issue in my book.

Anyone here have file system experience? I’d be happy to supply logs. Both from MacOS and diagnostics from the drive manufacturer’s tools.
I know it’s not actual corruption. My data is fine and the APFS read driver for Windows let’s me read everything on my drives.
so there’s some disconnect between the drive supplying the table/tree/data etc and Big Sur actually understanding it.

Have all of you done a clear install? i had issues and bugs (like ssd reading speed of 1900mb/s), because i have done an upgrade from mojave to catalina and than to big sur. With clean install of big sur everything is perfect, no issue, no spinning ball or freezing, and ssd speed is 2500 mb/s. Do a clean install ;)

Oh dear Apple - Big Sur is a bit of a disaster.

The whole point of Macs and MacBook Pro is the speed and efficiency. However, Big Sur should be called Big Slow. My MacBook Pro is now operating so slowly it is like going back to using a PC - probably even worse. On top of that, the MacBook keeps crashing - several times a times an hour - often two or three times in quick succession. It is very frustrating and very annoying.

Please get this problems identified in this thread of feedback about Big Sur sorted as soon as possible - i.e. at your earliest convenience. It is making using a Mac a total misery at the moment.

Big Sur has not been a successful upgrade of the OS.

I have the same issue as mentioned by everyone here. I contacted Apple support , they suggested creating a new user with admin entitlements to see if it's a hardware issue or a profile/data issue. Surprisingly, that worked! It's still going to be a pain in the neck to migrate 4 years worth of stuff to the new user but at least I can continue working

I’m also having issues after downloding MacOS Big Sur. My 2018 Macbook Pro has gotten significantly slower, the fingerprint authentication user login takes minutes and sometimes crashes and goes to sleep mode. Programs that used to run smoothly are now much slower and tends to become unresponsive and/or crash.

If Apple doesn’t release a fix for this soon I’ll call the support and demand them to fix the issue for me. Time is money friend.

@ javasol
Did you move admin to admin or user to admin in the new profile?

if this works it would be far easier than a full dress install.

I figure I’ll loose custom shortcuts and bindings.
aside from that anything else loss in a new account?

You mentioned needing to migrate to a new user and I’m wondering just how much would be involved.
granted I could probably just do it and see. I can always delete user 2 and go back.

but I’m trying to decide which would be the quicker solution. Like you, migrate nearly 4 years of settings, or find and fix the file system issue.
I've hit a wall with user-land fixes for the FS.

I hate this update!
The new big sur update has slowed down my computer to the point that I can simply NOT use it ! It’s ridiculous. I don’t have any system junk in my computer as I have the clean my Mac X software which cleans up all extra junk often.

I wish I had read these reviews before I downloaded big Sur. Like so many people here, my iMac has gone from running well to running slowly, freezing, or killing me with lag time. At this point I don't know that I will staying with apple. My friends with PC's do not have these issues.

Same Problem, also after updating to Big Sur Beta 11.1 RC. My imac ist not useable: starts very slowly, screen freezes while working...

iMac (2017, 3.4GHz i5, 8GB RAM)

This is completely unacceptable. I have the exact same issue with slow boot times on iMac 2017 1TB fusion. You pay for an expensive machine and you have the boot times of a 15 year old PC. It is supposed to "just work" without needing "hacking" with workarounds etc. These are professional tools. Horrible.

Same thing happened to me after updating to Big Sur. 2018 Macbook Air is now virtually unusable. Boot time is absurd, opening an app like Activity Monitor takes several minutes, and the computer freezes often. I tried setting up a new user account as someone suggested and barely managed to do so after about half an hour but it is just as slow. My very expensive computer is currently trash. Apple, please fix this!!!

same issue here but after a week of browsing trying everything, i solved this finally!!!!!!!!

so i got imac 2014, 8gb ram version core i5

full story here everything was okay, updated to big sure, lovely, then a day later everything started becoming unresponsive, type a letter, click on anything, it just frozen with the rainbow wheel, takes half an hour to startup

so i reset the imac, clean re-installed big sure, good for a day, then same thing started happening.

so i downgraded to mojave, good for 2 days, then suddenly samething again!

anyway, days of trying different things, reset smc, pram, removing one app after another, disable login items etc etc, i came across some one saying remove Avast.

Thats when it hit me, in big sur i had avast installed, then one restart later, the imac slowed down, same on mojave, so i removed Avast, now my imac is working perfectly well!!!!!!

Thank you erikxy! Removing Avast fixed it for me. Computer is now running fine with Big Sur. Hope this works for others as well!

Big Sur would not install problem free on my iMac 27 2017 (3.4 GHz Quadcore I5/1TB fusion/24GB). It hung halfway in a reboot loop, repeatedly giving the multi-language error message that something went wrong, wait for restart. After an hour I pressed shift, after which it continued and finished the installation and started Big Sur in safe mode. Performance was impossibly slow, peripherals could not be seen. Rebooting resulted in same error - iMac could only be started in safe mode, and slow performance prevented any practical use. Catalina had to be re-installed. Reverting to Catalina was also tough because the Time Machine restore would not boot, a clean Catalina install was required also. Next to the iMac on my desk I have a 2.4 GHz 2014 Toshiba laptop with SSD/16GB and Windows10 on a 27" UHD monitor, runs great - MacOS is beginning to be seriously less hassle free than Windows.

@Lostinlodos 

I just created a new user and gave that user admin rights. For the most part it's easy enough to migrate but if you have licensed software you now need to enter the license again

For me the hard part is that I have a clients microsoft remote desktop setup and that can't be migrated. Which means I'll have to ask the clients admin to login in to my desktop to set it up again, which is a real pain.

Everything else is just copying the files over and since the new user has admin rights you just need to run sudo with the cp commands

Me too, My iMac 27 inches retina 5k 2019 , Everything was slow down after update Big Sur. Please fix this problem.

THIS!

Big Sur has ruined my MacBook, it's unbelievable! My daughter's 6 year old Dell works faster right now!

Me too with a 2014 Retina iMac.
There were some quirks with Big Sur Release but 11.1 upgrade ruined the fun completely.
A separate account seems to help, but I am really afraid of moving all my stuff to one. I develop xplatform and created an installer setup with a Parallels Windos vm for my Mac compiled app – and I don’t, don’t, don’t want to set all the pathes manually again.

Disabling Dropbox and CreativeCloud brought some relief, but once I build apps things are starting to slow down again tremendously. But at least no kernel panics and no enforced user account relogins anymore for a whole day now.

I noticed that my Mac has a tendency to use only half of its memory. After one day of uptime, I still have almost 14 Gigs of 32 marked as free, but the system swap file is 3 GB in size,using half of it actively.
Shouldn’t it only start to page that heavily when RAM is really used up?

@UBogun That's what's frustrating about this. It's not CPU processing or memory consumption that's causing this slow down. If it would be I would be able to pin it down to a certain application or activity that's causing it. Like you, I still have most of the RAM free and CPU is not really working hard either. I get the feeling it has something to do with accessing the hard drive but I might be wrong

I also have now experienced this problem. My Mac has slowed to a point of my first Dell in 1990 on phone line. Even used Clean my Mac out of desperation. It helped somewhat, at least i was able to reboot in safe mode. This sucks. It is heartening to know I'm not alone and the problem is WIDESPREAD!!!! Damn you Apple...do something. my computer is worthless. I can now eat lunch in-between sites.

For iMac users seeing a slow down with Big Sur that are *not* running Avast:

1. Does your iMac have a fusion drive? (large spinning disk, small SSD cache 'in front' of it)

2. Did you upgrade from Catalina, from an older OS like Mojave, or did you perform a 'clean-install' of Big Sur by booting from a flash drive installer and reformatting the hard drive?

3. Is it possible that the fusion drive configuration has been messed up by the upgrade / reformat process?

If so, then your iMac could be effectively running directly from the hard drive alone - without the benefit of the SSD cache - and the fix would be to rebuild the fusion drive and reinstall from scratch.

After trying everything, the solution to the problem was to clean install and don't mess with Time Machine.

Big Sur messes up with the profile. So if you clean install and restore the profile, you restore also the slowness together with it. The best way is to just copy-paste all your files from a backup and install the apps from scratch. I did this and now my 27" 2017 1TB fusion iMac boots in 30 seconds!