The source should be mnt/Volume/Dataset -- so it will run from where you mounted your volume originally in Freenas. Freenas creates a dataset associated with the volume that you originally created (when you first set up Freenas), from what I recall. So source is mnt/Volume name/Dataset name (presumably Media?) -- it depends on what you called it, but this will be the folder/directory where all your media files are stored.
The destination can be anything you want that is in the jail, but /media is empty to begin with and is a great place to mount the folders from your source. What I gather the jail does is take the data that you have in your volume/dataset and remounts it where you want so that you can use it in your plugins within the jail. /media is just an easy and logical place to do it. The jail is essentially a small virtual machine that allows the plugin to run in a 'safe' environment. But, since it is 'separate' from the main operating system, you have to remount the Freenas data somewhere in the jail -- sort of like a symlink. That is what you do when you fix a destination. If you destroy the jail or plugin or the remount point in the jail your data will still be safe, since you still have the original volume/dataset that you created in Freenas.
It's been a while since I played with Plex, but I recall its setup being fairly similar to Emby. It might be that Plex prefers full path names, I just don't recall. Emby does use jails in the full path, but it isn't necessary to specify the full path when you set it up. There is a 'new' path from the mount point in the jail, and that is all you need to specify.
So, it sounds like you have things set up properly. It looked like you called your dataset associated with your volume Media. So, yes, for the source you would use mnt/Volume/Media.
For destination, again, I would use /media. You then choose which folders you want to associate with the different 'sections' in Emby from /media. You could choose another folder/directory in the jail -- like etc, bin, mnt -- and doing that would mount your media folder there. But I wouldn't do that because there are plenty of other files and folders in those directories and there is no reason to add new confusion. I know it sounds confusing to go from /mnt/volume/Media to /media, but that makes the most since. And, more importantly, it works.
ETA: I'm not entirely sure what you mean by being unable to let go of the smb share. You should be able to edit the path if you click on the library you created and use whichever path you want. But you can use the smb share to your advantage as a path substitute. So, if you set up Movies with a path /media/Movies you can also specify an alternate path \\FREENAS\Sharename\Movies (or smb:\\FREENAS\Sharename\Movies) just under the first path (/media/Movies) and that will work great. If that is what you are seeing in your library I would just leave it as it is.
ETA: I hope that makes sense. And Josh, Luke, or anyone please correct me if I have any of this wrong. I'm still learning how all of it works myself.
Edited by PhilWhite, 09 August 2017 - 08:28 AM.