Slow iMac problems

My iMac is now so slow as to be almost unusable.

It’s a 2013 iMac Intel (21.5-inch, Late 2013) 3.1 Ghz Intel Core i7 with 16 GB Ram and 1TB disk. (regular hard drive)

Symptom is that over time the Mouse gets unresponsive, jerky movement and impossible to see on the display in a smooth motion so very hard to use. I am mouse oriented don’t use many keyboard shortcuts at all as I’m faster with a mouse. I use a Dynex wireless mouse but I’ve tried with several different Logitech mice and even a wired mouse. I hate the Apple mice so I’ve never used them. Then even simple things like opening files and moving stuff gets slow and eventually it can take forever to do a simple task. The system takes between 8-15 minutes to boot up and about 5 minutes to shutdown. Safari gets to acting odd with solid black pages that only start to display the contents if I scroll over them and try to highlight them. Sort of a black screen encryption system I guess :wink: Time machine can take hours to do a backup whether it’s my external hard drive or to our Synology NAS server. I typically disable Time Machine during the day and let it run overnight to catch up. I do run a nightly CCC backup to an external drive. It can take between 2-6 hours to run.

If I leave it up for very long, over several days, it will crash with a kernel panic.

Rebooting will usually but not always help for a while.

I’ve run it in SAFE mode for a day and by the end of the day it was having the same problems.

I’ve run a full disk first aid on the internal hard drive and no issues were found at all.

I’ve run Clean My Mac on it and cleaned out all the various old software, no viruses found and nothing showing up on that scan.

Hard drive has about 130-140GB available.

I can run Activity monitor and the only thing taking lots of CPU is Activity Monitor itself and the kernel_task generally CPU is about 95-96% idle. Checking memory no swap memory is in use and typically only about 8 GB in use. Checking disk mds_stores has the most data moved at around 6GB.

I have not yet tried as another user as I need to move a lot of my data files if I plan to actually use it during that test. That was going to be my next step.

I’m running Catalina 10.15.7

By way of reference my Mac Air MacAir (13.3 inch ) 1.6GHz dual-core Intel Core i5 with 16GB Ram 1TB disk also running Catalina 10.15.7 works just fine. I’ve done most of the same types of tasks on it and it also is doing time machine to an external spinning hard drive and to the server but never bogs down nor crashes.

After the another user test (which I hope to complete today) I was thinking first try to reinstall Catalina. Then I was guessing a nuke and pave but that’s going to be nearly a week of work and I’m wondering if I should try something else first.

Any suggestions.

Maybe your HD is beginning to fail. My wife has the same machine (with 8 GB RAM). Because it was so slow, we started using an external SSD as the system disk and the internal just for storage. We did this in 2014 and it’s only now starting to show its age. Won’t be able to run Big Sur.


The hard drive may be compensating for any issues it is having, thus the first aid didn’t show anything.
I would go with @neonate’s suggestion of using an external SSD.
It really does sound like the drive.
Do you have a stethoscope? Try listening to the iMac and see if you can hear the drive making noise as it tries to reread areas of the disk. You might also press you ear against the case.

I’m a livestock farmer. I think I have 3 or 4 stethoscopes around from cheap ones to a really fancy one my vet got for me. :grin: And nope, none of the normal hard drive on it’s way out noises at all. I also did the hand on the hard drive area test for heat and other vibrations that you can sometimes feel before you can hear them. Nothing sensed.

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I had similar symptoms on a 2015 iMac with a spinning drive. I copied the system drive to an SSD in a USB caddy, and started booting from that. The symptoms went away, and the iMac is transformed. (I believe you should be able to buy a 1TB external SSD for not much more than $100 (look for the SanDisk Extreme Pro 1TB as a good example), but I’m in the UK so I may be out of date on that.) If your Mac only has USB-2 and not USB-3 you won’t get quite the same performance boost, but it will still be spectacularly quicker than your current drive.

Even if that doesn’t solve all your problems, the investment in the SSD is worthwhile, and it will be easier and quicker to solve any remaining problems than it could be booting from a spinning drive.

When you restart after the kernel panic you get some log info, right? What does that say?

I’ve never seen any log info. The system says your Mac restarted because of a problem do you want tossed info to Apple and that’s about it.

Yes, the info to be tossed to apple is what I’m looking for.

To be honest I don’t think I ever looked at it beyond kernel panic I just say I was just using the machine normally and hit send. It happens so often it’s almost an automatic response for me.

Catalina has had issues with kernel panics since it was introduced. Supposedly they were fixed in 10.15.7 but who knows. Take a look at this:

I’d be interested to know if zalloc is mentioned in your panic trace. If so, that’s likely a kernel memory leak and not your disc. Your description of the machine getting progressively slower sure sounds like a memory leak to me.

Can you check the temperatures of the cpu? You may be reaching 98°C at almost idle load causing it to thermal throttle.

That it is my current problem on a 2014 iMac 5k which I’m planning to clean very soon (already ordered the required parts). Dust over years (worse if you have pets) can really clog the iMacs cooling system. You can check it with menubar stats, if you are hitting really high temperatures without much load it is probably your problem too. If that’s the problem you can use the chance to replace the hard drive for an SSD and give it an enormous performance boost.

I haven’t had any zalloc-related kernel panics (or any, I don’t think) since installing 10.15.7.

Me either, but the symptoms @OogieM describes sound very much like a memory leak to me. Howard Oakley has written about some machines silently refusing to update their firmware, hence my “who knows” remark.

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Have you experienced kernel panics in this situation?

It hasn’t gotten to that point yet, not even hangs. Just everything slowing down and problems moving windows , the cursor , etc… temps are around 75°C at idle and raises to 98-99 as soon as the cpu goes over 25%. it happens faster as time passes. I know that it’s dusty because I’ve blown compressed air trough the bottom vents and a ton of dust came out. I also have two cats and they like sleeping next to the computer so I’m pretty sure it’s filled with dust and cat hair and the lower vents are not enough to properly clean it.

I’ll try to record a video when I open it, or at least take some pictures and post them back here.

@OogieM have you check the temperatures? Black screens in safari may be related to the GPU overheating.

OK Got the trial app iStat Menus and am running it. Not doing anything CPU proximity, cores and CPU are all between 131-140°F about middle of the range on the app display. Fan is between 1300-1400 RPM

The system takes between 8-15 minutes to boot up and about 5 minutes to shutdown.

@OogieM that’s way too odd. As already mentioned, could be the HD failing. I had a 2012 MacBook Pro and boot up and shutdown times were never longer than a minute or two.

Get an external SSD drive or a SSD disk+enclosure, you’ll definitely notice the difference

In that case it’s probably the hard drive as most people are suggesting. In mine is definetly a heat issue. What temperatures does it reach when you open a video or two in youtube?

No major changes,

OK Here’s an update:

Boot off external hard drive, things run very slowly as expected. Made 2 full complete bootable backups (took over 36 hours!) Boot off one of them and then restore from the backup. No change.

Boot off the external again, reformat the internat drive, reinstall Catalina, migrate my user info over via Migration Assistant. In testing now. Still very slow to boot up. Am having all sorts of permission errors for some reason. I can no longer log into the mac to move files back and forth from my laptop yet I am using the same username and password and permissions appear ok with read and write for te usernames I am logging in with (have tried 2)