From: Lists lists@benjamindsmith.com
Our next big test is to try out ZFS filesystem send/receive in lieu of our current backup processes based on rsync. Rsync is a fabulous tool, but is beginning to show performance/scalability issues dealing with the many millions of files being backed up, and we're hoping that ZFS filesystem replication solves this.
Not sure if I already mentioned it but maybe have a look at: http://code.google.com/p/lsyncd/
JD