I have two java applications (openhab2 and eq3 occu) on an ubuntu 18.04 machine that are doing some background activity. I would expect this to happen in memory. But for both applications iotop is showing a disk write operation approx. every second.

  • I'm running laptop mode tools which set the filesystem parameters and hdparm to spin down the disk even if there are changes to files and write them later.
  • I moved all log files to a folder in tmpfs.
  • I turned off swap, as there is plenty of RAM in the machine.
  • With /proc/#pid#/fs I can't see any open files which would be written.
  • find -mmin 1 is not showing any updated files.

As it happens for both applications the same way, I suspect that the java jvm is doing something on the disc directly.
Behavior is the same whether I use openjdk1.8 or oracle java 10. I tried to use G1GC. That reduces garbage collection efforts but doesn't let the disc sleep, either.
Could anyone give me a hint, what I could do to find out what is happening here?
Thanks a lot!