I have a feeling its Plex, and I am tempted just to shut Plex down for a few hours (its on a separate machine) to see what happens.  Active streams shows nothing connected.  But my disks have been spinning for days. When I click "spin down all" they all come right back up within seconds.  I was running Plex on a linux machine some time ago and never had this problem, now I'm running it under Windows -- could it be something Windows is doing?  I have mapped the media shares on the unraid server to drives on the Plex server.

 

Is there any way (from the command line) to see with a degree of granularity what is keeping the disks spinning?

 

Thanks.

Use "inotifywait". You'll need to instal a package.