NAS to NAS backup (Drobo specific hopefully)
Good question (and good cause to create a NAS-specific Q&A forum here... I moved your post, @podfeet!).
Is there no longer a 'copy' app on either of your Drobos? Speaking of, which model Drobos do you have? I just found it on my Drobo 5N in the Drobo Apps > Other Applications section. I think it's exactly what you want (but I could be wrong!).
Alternatively you could go in and use 'rsync' from an SSH session, but obviously a little smoother/easier to do it in the GUI/app.
w00t - glad you created a NAS section @davehamilton. Seemed like there should be one.
I've got a 5N and a 5N2, with my desire to back the 5N2 up to the 5N. I don't see Copy on either one of them in the new firmware. It's highly improved lately, btw. Pretty icons and better sorting.
Ok, I must have installed copy on my Drobo from a 3rd-party source. I've checked both DroboPorts and DroboWorks and... nada. Interestingly, if I search for 'copy Droboapps' I find a link to http://www.drobo.com/drobo-solutions/drobo-apps/copy/ but... it doesn't go where one would expect. Maybe this has been deprecated.
And sadly that's a common occurrence on Drobo's website. There are lots of dead links. Their support pages where they store their manuals has been down for at least the last 5 days (that's when I notified them and they said they'd "get right on it.")