Comment by BanAntiVaxxers
2 days ago
You could have three parts to this "black box".
Part A emulates a USB drive to Device A.
Part B emulates a USB drive to Device B.
Part C is the eventually-consistent synchronizer. It can "see" into Part A and Part B.
If file exists on A but not B, copy the file from A to B. If file exists on B but not A, copy the file from B to A.
To each device, the files magically show up.
To resolve conflicts, it would have to do it based on timestamps.
The synchronizer could be anything. Heck, it could even be rsync. This device could be 3 Raspberry Pi's crammed into a single box.
I would happily pay $100 or so for a device that could do this.
Yes, it could work. You would have to "disconnect" A and B for files to magically show up, because the drivers on A and B don't expect the filesystem to change "under their feet". It doesn't monitor the disk blocks for changes and rebuild directory indexes, file tables etc.
If you want a truly "automatic" solution, your magic USB device would have to pretend to be a network device to both A and B, perhaps with DHCP or ipv6 autoconfig, and export NFS and/or Samba to both ends.