I'm running MacOS High Sierra and just got a new 3TB external USB hard drive. On this drive, I have set up one 500GB encrypted MacOS Extended volume. I also have another 500GB portable external hard drive, which contains one 500GB (also encrypted, also MacOS Extended) volume.
I would like for the two volumes to be in sync with each other. There's a catch though: it has to be a two-way sync. So if I update or delete files on one drive, the changes have to be copied to the other.
There's a second catch: the drives will be connected at different moments. I want the synchronization to happen whenever both drives are connected.
Does anyone know of a tool that will allow me to do this? Unison seems a pretty close match, but I'm not sure how to set it up so that it checks whether both drives are present etc.
repeat = watch
option), or only sync every few seconds or minutes or something.