When I rsync data from one Pi to another, I was getting an average speed of 700 KB/s. Thinking this was some sort of network bottleneck, I simply took the HDD from Pi 2 and put it on Pi 1, which means Pi 1 was thereby hosting both of the USB HDD's. I then rsync'd the data from one drive to another locally on one Pi. Still, I had terrible performance of about 700 KB/s.
I already have SSH keys set up. When I ran it over SSH, the command was:
rsync -az --delete --progress /media/storage/ email@example.com:/media/storage_II/
And when I had both drives in a single Pi, I ran:
rsync -az --delete --progress /media/storage/ /media/storage_II/
Each Pi is connected by a tablet charger of some sort. One is for an iPad (5v, 2a) and the other is for a Galaxy Tab (5v, 2.1a), so they should be getting ample power.
I then got frustrated, so I plugged both of the hard drives into my desktop. I rsync'd all of the data at about 18-20 MB/s, significantly faster than the 700 KB/s I was getting before when using the Pi's.
As a result, I'm questioning some things here. Is this the intended performance of the Raspberry Pi? I understood that there was some sort of relationship between the LAN and USB chips, thereby sharing bandwidth hub style, making USB performance seem significantly slower than the traditional USB 2.0 speeds we're used to. Is that likely the case here? If it is, fine, but if there's something I can do to speed things up I'd certainly like to.
Appreciate the insight!