What is spinning my disk up periodically?

I recently bought a CubieBoard 3 and installed Debian. The OS is installed on SD card and I use a 2.5" HDD to share files. The HDD is using ext4.

I want the HDD to spin down if it is not used to save energy and increase the disk's lifetime. I had some problems using hdparm so I tried hd-idle which seems to work.

The disk is spinning down for exactly 5 minutes and is then active for other 10 minutes just to repeat it again.

Any tips how I could analyze what is spinning my disk up?