I'm going to try this tonight.
1. I have my main LR5 catalogues on a MacPro 4tb raid (0+1). It's backed up by time machine to a 9tb Synology NAS (SHR)
2. I'm hooking up a 6tb Synology NAS (0) to it and I'll back up the pictures and documents from the MacPro and the Music from a separate Synology NAS (SSD, 0). Once it's all loaded, I'll move it to my office and set it up for backup over the internet. It's NAS to NAS, so, I may have the Lightroom/picture files and the time machine backup on the 9tb NAS.
I'll have an on-site and offsite backup that's run every day.
3. I'm hooking up a Seagate Backup Plus Fast Portable 4tb drive to the MacPro (no Thunderbolt on mid 2011 Mac Pro). I'll use ChronoSync to copy and synchronize the Lightroom catalogue and picture files (2.6tb at present). I believe, if I hook it up to my MacBook Pro, I could open the Catalogue that's on the external drive (will it find the photos?). Any changes that i make in those catalogues would then be sync'd back to the MacPro when I hook the external drive up to it and run ChronoSync.
I think this will work? BTW: I think the Synology Drives are faster then the Drobos.
Cheers, Matt