Remote replication

It's simplest if he has separate Hong Kong and London folders (for music ripped in those location). Otherwise, music would be hard to delete.

If that works for him, then frontview backup jobs could be used - syncing the Hong Kong folder from Hong Kong->London, and vice-versa for the London folder. rsync over ssh is secure, but would require some port forwarding in the two routers.

Even though the music is already available in both sites, the initial backup/sync will copy it all over the network again.

iaincbrown wrote:
He wants to rip music in either location and have it available when he travels to the other location. He has a ReadyNAS Pro4 in each location. He runs MAC (Mavericks) at each location How can I set up the system to remotely replicate between each site.

If it were me, I would just run BTSync on the two Macs to keep their music folders synchronized: http://www.bittorrent.com/sync

Experiment with a small test folder first, and also don't forget to implement a solid backup system. Once the folders are synced -- regardless of the method you use -- a user error at either location will have the potential to damage or delete the files in both locations. (Although you can decrease the chance of disaster by, as StephenB suggested, creating two folders at each location and performing two one-way sync operations [BTSync calls this "read-only sync"] rather than one two-way sync).

a two way rsync could do the trick I guess.
From what I know Rsync erase files only if the destination is older than the source when you use the update option. Problem is if he deletes domes files, then the --delete option will be a problem since if the first device do initiate the sync lack some files they'll be deleted from the other device too.
A quick research on "two way rsync" shows up a software called "unison", seems worth checking. (http://www.openlogic.com/wazi/bid/188061/ ) Didn't try but looks interesting.

If you are using frontview, then you either "Remove deleted files on target" or not. If you select this, then sometimes rsync will mistakenly delete new files(assuming you are scheduling one rsync job in each direction between a pair of shares). If you don't, then files are never deleted.

iaincbrown - do you want to stick with facilities that are already in the pro, or are you willing/interested in installing add-ons (possibly via ssh)?