How to switch file systems with least downtime?

I don't know if this makes any difference, but my pg_xlog directory is on its own volume as well, so I would have to unmount it and remount it as well, but I would not have to copy over my xlogs.

I figure the first part of this is to do a pg_start_backup() and rsync the files over., bu I'm not sure what to do after that.

Thanks for your help.