Not sure if this is a problem but I noticed that my disk 3 (WD 3tb red) shows what appears to me as excessive reading. It's attached straight to the motherboard and no special settings have been made for it. Is this normal?

 

screenshot attached

 

Do you happen to have your server exposed to the internet?

No but there's a folder that I don't need with a huge amount of small files and I think cache_dirs keeps hitting it. Gonna delete the folder and see if it stops.

Disable cache_dirs;  or set it to ignore that folder;  or simply delete the folder if you really don't need it.  Then do a  "Clear Statistics"  to zero all the stats, and see if you're still getting background reads.