Let me know how it goes.
Well this is about to go out the window....what appeared to be relatively straightforward is not, for me anyway!!
Ok, I can set up the remote plugin referencing the share on the other omv, that appears in the file system, I can add a share under shared folders for the destination, however, I can't add a share for the remote without an error....this...
I'm assuming one has to do this so that you can reference this in rsync.
I can create a share on the usb pointing to the destination, but because I seem to have lost the plot, I thought I would start again....no such luck I can't delete the share that points to the usb!!
At present I seem to stuck and wondering if this was a good idea.
EDIT: Done a clean install....but I'm still getting the same error, 'failed to set file group to users', there is something I am not doing. I have set up the remote plugin both with a user Backup as you suggested and without i.e. guest doesn't make any difference same error.