Yes, I saw it late and then processed my post. I don't use telegraf.
There is also no activity on the hard drives, only on the SSDs, but that's how it should be. It's strange when I manually put the hard drives on standby, they stay in that state.
As indicated, I haven't changed anything after the update from 6.8.3 to 6.9.0 that could influence this behavior :(.