Synchronize two working external drives over network
This ServerFault entry asks a similar question. The answers there are rsync and a product called Unison. It sounds like either solution fits the problem you have in front of you.


For rsync, something like the following recipe would likely work (I haven't run this, so the syntax may need some fiddling):

# sync drive.2 to drive.1
rsync -av --stats &lt;user&gt;@computer.2:/path/to/drive.2 /path/to/drive.1/

# sync drive.1 to drive.2
rsync -av --stats &lt;user&gt;@computer.1:/path/to/drive.1 /path/to/drive.2/

And Unison, the other option from the ServerFault entry, looks like it's a software package designed specifically to solve your type of synchronization problem.