Array never spin down

[Eideard]

Hello,
I have a small problem.
I have 6 HDDs in the array and 1 M.2. NVME as cache. The shares domains, system and appdata are located on cache and are set to prefer: cache.
Normally the HDDS should shut down after 15 minutes but they don't. Something is written to disk 1 every 3-5 seconds, but I can't figure out what. Is there a way to find out what's happening there?

[Squid]

1 minute ago, Eideard said:

The shares domains, system and appdata are located on cache and are set to prefer: cache.

Sure about that?  You can confirm via Shares, Calculate.  You also have to remember that even with prefer cache, any open files cannot be moved

[Eideard]

Hey, yes i'm sure.

I have copied all files manually to cache.

But i've checked it now, all Files of that shares are on cache. I have added a screenshot of "system"-Share. 

 

My guess is that some system just streams for a very short time. So I can't see it in the GUI. But how do I find something like that? IP or Filename would be enough for me.

[Squid]

Posting your diagnostics might provide a clue.  Some apps (notably Nextcloud / Owncloud) are notorious for stuff like this

[Eideard]

Oh damn,

you say nextcloud and now i begin to see...

i think, i found the problem...

For testing, i have mounted a share in my Nextcloud VM. A sync process was running in the VM and looks all time on the share... i've unmounted this share and after 15 Minutes the disks are offline...

 

i'm so sorry! Accidentally you gave me the crucial tip. Thanks!