Something unknown reads data from my disks

I've got a small server at home to access my files and the HDDs don't spin down. Currently it runs Ubuntu Server 22.04. Executing something like $ cat /sys/block/sde/stat displays some information including the total sectors read. If I wait for about 20 minutes and execute this command again, the total amount of sectors read increased.

$ cat /sys/block/sde/stat
 6886729 970027822 7822380784 1292509782    15759   276608  2297706   485868        0 30475568 1293440472        0        0        0        0    23680   444820
... Wait about 20 minutes
$ cat /sys/block/sde/stat
 6886734 970027822 7822380787 1292510398    15759   276608  2297706   485868        0 30476188 1293441088        0        0        0        0    23680   444820

But in theory there shouldn't be any process accessing this HDD.
This all started 2 days ago after upgrading to Ubuntu Server 22.04 from Ubuntu Server 20.04.

I already tried to use <inside the correct directory>$ sudo fatrace -c, but this didn't show anything. Also I tried to use $ inotifywait -m -r /..., still nothing.

How am I able to dig deeper so my HDDs are finally able to spin down again?

Using iotop

You can monitor disk IO with iotop.

Install with:

sudo apt install iotop

And run:

iotop

This should tell you exactly which processes use disk and swap.

Using htop

You can also monitor IO directly with htop (although it's a sort of "hidden" feature).

Install with:

sudo apt install iotop

And run:

htop

Now press Tab to switch to the IO screen (instead of the main screen). This gives info similar to iotop.

Using udisksctl

If you suspect the activity is related to udisks, you can try and run:

udisksctl monitor

This will tell you if there is activity with the udisks daemon.