OS3 only provides share syncing via the web GUI.
You could use rsync when both have SSH enabled.
Example where we SSH into boxA (with user sshd)
# list home dir contents (note the : at the end)
rsync sshd@IPaddressBoxB:
# list root dir contents
rsync sshd@IPaddressBoxB:/
# actually sync stuff from BoxB to local /opt dir
rsync -a sshd@IPaddressBoxB:/opt /opt
# switch the arguments to sync local /opt to remote /opt
# setup ssh keys if you don't want to type passwords
I wouldn’t sync /etc and the home dirs… might mess up private keys.
Also the /proc and /dev doesn’t need syncing… and /tmp is not interesting either.
Note: syncing your root dir is a bad idea in general.
EDIT: oh I see you just want to sync the whole share.
rsync -a sshd@IPaddressBoxB:/shares/someshare /shares/someshare