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My MacBook (2016 with TouchBar) running macOS 10.13 has a 512GB SSD. Looking at the activity monitor after a couple of weeks of uptime (most of it spent in standby), kernel_task shows 1.43TB (!) of bytes written to disk right now:

Screenshot of activity monitor

What is wrong here - how can I diagnose why kernel_task is writing so much data to the disk? (This happens all the time after each reboot).

Memory pressure is still "green" most of the time. Running out of space is also not an issue so most of the data seems to be "temporary".

However, I am a bit worried about my SSD - writing 25 TB per year (in addition to the "regular" workload) does not seem to be a good idea...

Any ideas?

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    Pro Tip: Cmd/Shift/4 for screen capture... tap Spacebar, the cursor changes to a camera icon & will capture any window you click, complete with nice drop-shadow.
    – Tetsujin
    Commented May 18, 2018 at 12:14
  • Have you looked at this answer? apple.stackexchange.com/a/291168/22382
    – ajmccall
    Commented Dec 17, 2019 at 14:53

3 Answers 3

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I had the same issue on my 2010 MacBook Pro.

The fix for me was to clean out the dust from inside my laptop. I removed the fan (just requires unscrewing it with a special screwdriver, like the type for installing a hard drive) and there was a giant amount of dust blocking the airflow.

The kernel_task process helps regulate the computer temperature. It was trying, but the fan couldn't do its job. After this fix, I went from 500 GB of kernel_task disk usage within a few hours of computer use, to less than 2 GB.

Interestingly, this also seemed to fix the issue of distnoted and sharedfilelistd processes using too much CPU.

However, my computer didn't have massive disk usage from the CrashPlanService process, so you might have a different issue.

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    Dust can certainly build up inside machines, and that's a very likely cause for overheating (and, eventually, CPU throttling). If you can clear it out safely, that's probably a good idea. But how can that affect the amount of data written?
    – gidds
    Commented Apr 20, 2023 at 16:04
  • I agree with @gidds that it's quite unclear how improving a laptop's thermals by removing disk would result in fewer disk writes.
    – Chris
    Commented Jan 27 at 2:21
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This is because the system is constantly swapping SSD for RAM, writing for moving data from RAM to SSD, reading for the moving it back.

The root cause is RAM is not sufficient...

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I just got through a several day battle with Time Machine and possibly an APFS bug on Mojave that was also leading to terabytes of data being written over the course of just a few days. It's kind of funny, yet sad, to see the kernel_task process at the top of the disk usage charts in Activity Monitor. (It has currently leveled off at "1.38 TB" on my wife's 2014 Mac Mini with fusion drive.)

For me, I had to spend copious amounts of time mentally processing the output of the sudo fs_usage -w -f diskio command. I noticed that the backupd process was looping around reading metadata for the same two files of a particular application that I no longer used (Android File Transfer).

After deleting that application from my machine and then removing several older Time Machine backups from several years ago using the tmutil delete command, I was able to defeat both the backupd metadata read looping issue as well as the inordinately excessive metadata writing directly to my HDD from the kernel_task process.

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