Syncing to and from USB2 hard disk

[HPG]

I think this question has been answered in another post, but I wanted to be sure. I'm planning to use SFFS to sync hard drives of different computers, using a USB2 hard drive which I take from one machine to another. That means I need to be able to sync in two directions for each machine: first, when I arrive at the machine to update it, and the second time when I'm leaving and I need to update the USB drive. The biggest files to sync are typically Thunderbird mailbox files and their associated .sqlite file, which can be between 400MB and 1GB or so.

My first thought was that partial file copying would be helpful because USB2 connections take a bit of time to make these large-file transfers. However, I see that for Mode 1 partial updating, it is very important to make sure that nothing changes the destination files, and of course if syncing is taking place in both directions this will happen. Mode 2 allows this, but I don't see how to make it work for a plugged-in USB drive; it seems to be written in terms of syncing with a remote computer.

Then I found a posting that seems to suggest that, for USB2 connections, there's probably no speed benefit to partial updating anyway because the process of checking for partial changes takes as long as making full copies. Is this correct? In other words, for the situation I describe, is it true that there's no need for a partial update solution because it wouldn't speed things up?

[superflexible]

Correct, you cannot gain anything with Partial File Updating in this case. Please leave it turned off.

[HPG]

Many thanks for such a quick response!