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iMac with sudden Performance Issues

After upgrading to macOS 10.15.4, my iMac (27-inch 5K 2015) began running very slow. After doing a full restore back to a Time Machine backup of 10.15.1, the performance issues unfortunately didn't get fixed. Booting up and getting to the start screen takes much longer, as well as starting up apps or even opening a macOS window results in endless beachballing. Almost every app that is more demanding than Safari will start hanging and stop responding before it has even opened. The Mac has become unusable.


Looking at the Activity Monitor, my processor and RAM (7GB of 24GB used) should handle this easily, which it always has. I tried re-indexing Spotlight, performing First Aid on my disk, resetting SMC/NVRAM/PRAM, resetting permissions among other things. While I expected my Fusion Drive could be the culprit, the Mac's Diagnostic Test returned no issues found with any of the hardware.


I also ran an EtreCheck, which came back with the following results:



Anyone has an idea as to what could be the issue plaguing my Mac?

iMac 27", macOS 10.15

Posted on May 19, 2020 4:07 AM

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Posted on May 20, 2020 3:25 PM

Boot into Safe Mode (How to use safe mode on your Mac - Apple Support) by booting with the Shift key held down and check there to see if the problem persists.  Reboot normally and test again.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing some system cache cleaning, volume verifying and directory repairing. 


Additionally if necessary download and apply the macOS Catalina 10.15.4 Combo Update 


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Question marked as Top-ranking reply

May 20, 2020 3:25 PM in response to Casperster18

Boot into Safe Mode (How to use safe mode on your Mac - Apple Support) by booting with the Shift key held down and check there to see if the problem persists.  Reboot normally and test again.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing some system cache cleaning, volume verifying and directory repairing. 


Additionally if necessary download and apply the macOS Catalina 10.15.4 Combo Update 


May 19, 2020 11:19 PM in response to BDAqua

Yes, I tried restarting the Mac. But still, the performance is poor.

I am worried that it is in fact the HDD. Since I have had issues with this drive before. Is a HDD in a failing state something the Apple Diagnostics Test does not pick up? Can this be repaired, or would the drive need to be replaced?


Here are the results of a second EtreCheck:



May 21, 2020 9:13 AM in response to Old Toad

In Safe Mode the issue still persists. Per your advice I also installed the macOS Catalina 10.15.4 Combo Update, but yet again with no results. If anything – it made it slower. I tried running 10.15.4 in Safe Mode, so nothing was launched and ran another EtreCheck:


Everything from booting up, to loading Launchpad, to opening a folder. Everything freezes or takes ages.


Appreciating all the help – thanks!

May 19, 2020 3:23 PM in response to BDAqua

Thank you both a ton for the help so far – I appreciate it.


Per the mentioned thread and advice I have fully removed both CleanMyMac X and Torrent-related apps from my Mac. I also checked the leftover files through Find Any File and deleted them as well. Unfortunately, after rebooting the Mac is still unbearably sluggish. Failing to simply load any app. Occasionally, even macOS itself seems to get clogged by removing desktop icons or the top bar becoming invisible.

May 20, 2020 1:39 PM in response to BDAqua

Exactly. I'm puzzled.


Through Activity Monitor, at the time of checking, the 'remindd' process was taking up a consistent 100-110% of the CPU (and has been running since bootup, according to the CPU time). After force quitting the process the issue didn't go away though. Apart from that I regularly have 70-80% inactive CPU usage.. RAM is also in the green at all times, and power consumption doesn't look off either.

May 22, 2020 5:56 AM in response to BDAqua

Thankyou all for your help. I have tried doing a full clean install of macOS and seeing if that solves the issue. From Disk Utility I right away noticed the Fusion Drive got splitted to SSD + HDD so I had to restitch them. Weirdly enough, it prompted me to install the original OS (OS X El Capitan). Upon doing so the installation went well. Then I restarted the Mac and sure enough was greeted with the following error:


'OS X can not be installed on your computer.'

POSIX-diagnosis: The operation couldn't be completed. Input/output error.


So then I separated the Fusion Drive manually into SSD and HDD.


Tried installing OS X on the pure SSD, and it worked wonderfully. Albeit older software, it ran as fast as the Fusion Drive did before all the issues started appearing. Ran an Entrecheck and it finished within 1:36 as 'Excellent Performance'.


So, I then tried the same for the HDD. Getting it to be reformatted on Disk Aid took very long. Installed OS X, but upon rebooting it wouldn't do anything. It would be stuck with a loading bar and the Apple-logo. Then I checked which drive was the boot drive, and the HDD would not even show up. Eventually resulting in: 'An error has occurred during installation.'


Disappointed that I can not check the speed on the pure HDD and compare it to the SSD. Nonetheless I am now convinced that there is enough evidence to claim it is not the software. ;)


Am I right to guess the HDD is the issue, although it shows up as 'fine' through the Diagnostic test?

Also, if I were to replace the old HDD with a new SSD, what should I do with the old NVMe SSD of the Fusion Drive?

iMac with sudden Performance Issues

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