OK, I must be missing something. Here's my environment:
I have OMV installed and running and patched with latest updates.
OMV is installed to a 30GB SSD drive formatted EXT4.
I have a pair of SATA drives in a RAID1 array for my DATA formatted EXT4.
I have an external USB drive formatted as ext3 with volume label /usbext. The drive has several folders and data on it already.
I installed the rsnapshot plugin wanting to backup my DATA share to the external USB.
I ssh'd to OMV and manually mounted the external USB disk to /media/usbext.
In the OMV gui, I see the exernal USB under Storage, Physical Disks and under File Systems it shows the external USB is mounted and online but not Referenced.
In OMV gui, when I go to Services, Rsnapshot and try to add a backup job, I can select my data share for the Source folder but I see no way to add the external USB drive as the Target folder. The Target folder only shows shares from my DATA volume.
I guess I am overlooking something. Any ideas?