Multi-Threading?

[CACook at quantum-sci.com]

I have a backup server now restoring 6TB of data to a client machine.  This has been going on for four days now, and no sign of getting close to completion.

The connexion is Gb enet end-to-end, and is running at only 40Mb/s.  It has far more capacity than that.  The only limiting factor I can see is on the backup server one core of the CPU is running 100% rsync.  Clearly rsync is not multi-threaded.

In researching this I find that a change to multi-threaded goodness would require a massive rewrite, and would only be considered for an rsync replacement.  

Is there such a replacement in the offing?  Is there any sort of workaround for the time being?  ATM the large amount of data is the /home directory on the client machine.