I have a DS411j. Plex media server on my mac mini has no problem seeing the other drives in the NAS, and one of them used to be the 'movie' folder. I added a 6Tb HDD with the intention of keeping the movie folder on this, but PMS does not see it when I try to 'add folder', and 'browse for media folder' through the web interface. I'm guessing this may have something to do with permissions. I've been through the 'share folder' settings on the synology to ensure read/write access, and the 6Tb HDD seems no different to the other HDDs in this respect.
Any ideas how to fix this?