borg does either use a directory as repo (no matter whether local or mounted via network fs) or works client/server via pipes that are usually over ssh (in that

borg does either use a directory as repo (no matter whether local or mounted via network fs) or works client/server via pipes that are usually over ssh (in that case, it needs a remote borg process to talk to). instead of ssh, one could also use anything rsh-like, but of course ssh is the best option here. no sftp inside borg (nor anything else).