Copying files between linux machines with strong authentication without encryption

You tried doing what I normally do, using a lower-weight encryption algorithm (like arcfour). When that becomes the bottleneck, the next approach I use is disabling ssh encryption entirely.

One approach for this is to use hpn-ssh as your transport. My normal application for this is SSH copies across high-bandwidth, long-distance links (e.g. a 10GbE link between Chicago and New York with 16ms latency). hpn-ssh allows tuning of TCP windows there, but also has the option of disabling encryption entirely. That may help in your case.

Also see: Why is my rsync so slow?

A couple of quick-fix options come to mind:

• Stagger your backups so that they aren't all running at the same time.
• Replace ssh with hpn-ssh (on the server and all 70 machines) and use its NONE cipher, which turns encryption off after authentication is complete.