Kernel Task Writing Large Amounts to Disk

[cheezypuffs]

I've had twice now where I check the bytes written and it's gone over 5tb in just a few days of light use. I feel like something happens when I leave windows open overnight / for a few days- but not using the computer- but can't find any consistency.

Also, I have the same exact computer at work (Mac Mini M1, 512GB/ 16GB Ram) and I leave more stuff open on it, and I've never come close to these numbers on that machine.

I recently wiped this drive clean and re-installed only a few apps. Nothing different on the two machines, not sure why this is happening.

Any thoughts? I know this was a known issue but was it hardware related? Thanks for any insight.

(I have a case open with Apple but haven't called them back yet because I have spent so much time with them with prior issues it's just exhausting.)

 

[Mike Boreham]

You will get more perspective by starting near the end of this huge thread:

https://forums.macrumors.com/threads/ssd-swap-high-usage-of-terabytes-written.2284893/

Your first sentence is correct....."Can't find any consistency"

Lots of people think they have found causes and now to avoid it, but there is no single cause or solution.

For some people it is a steady usage, for others like me there have been rare rapid bursts (28TB in 31 hours) With no explanation and not obviously noticeable while occurring.

It might only be an actual machine life problem for a tiny number of people who are seeing exceptionally high usage, and then only after a few years.

I wouldn't lose any sleep over it but it is an interesting phenomenon.

 

[joema2]

I've had twice now where I check the bytes written and it's gone over 5tb in just a few days of light use. I feel like something happens when I leave windows open overnight / for a few days- but not using the computer- but can't find any consistency...

Have you ever installed SoftRAID? If so it might be the problem. You can check that by Activity Monitor>Disk and monitor writes by kernelmanagerd. That is the host process that loads kernel extensions. If it keeps going up at about 2 MB/sec (or more) in the absence of other activity, it might be that problem. In my case it was about 1 TB of writes every 5 days.

Since kernel extensions are now deprecated, over the last few MacOS versions there have been various changes to how those are handled. It seemed to happen or get worse on Catalina and Big Sur. It might have been caused by interactions between the SoftRAID kernel extension and others such as from HP. For that and various other reasons I finally got rid of all SoftRAID.

Whether caused by SoftRAID or not, when faced with anomalous mysterious I/O, you can watch it's doing with the terminal command fs_usage. Procedure:

(1) Use Activity Monitor to get PID of kernelmanagerd (say, 117 in this example).
(2) Syntax: sudo fs_usage pid 117 > fs_usageoutput.txt (where 117 is for example the PID of kernelmanagerd)
(3) Run for about 60 sec then abort with CTRL+C.
(4) Examine output file with a text editor or the command-line tool "more" (f goes forward one page, b goes backward one page, h for help).