The situation: 2 computers, each has a large section with data on it (the OS and programs are in other sections on the computers and can be ignored). The data should be the same on both computers, so when parts change on one computer the change has to be mirrored by the other computer (within a generous time-frame, say a week). It is not possible to create a network connection between the 2 computers, but I can attach an external drive.
Is there a tool to keep the 2 data sections synchronized using an external drive, where the external drive is much smaller than the data section (e.g. the external drive has only 10% of the size that the data sections have)? It can be assumed that the actual changes easily fit on the external drive, even in the sense that all files that changed (not only the changes) easily fit on the external drive.
If it makes things easier master-slave synchronization would be sufficient, ie only one computer can change data.
I could imagine an approach where the transfer drive stores a DB of time-stamps / checksums of the data files and only stores those files on the external drive that actually changed and need to be updated on the other computer; but I don't know of an exsiting tool that would do this, or solve the problem with a different approach.
[Edit] Note also that the computers are not at the same location, but several kilometers apart.