The Apple knowledge base note on this question says to hardwire the Time Capsules and a computer together through ethernet, and transfer the data from TC1 to the computer to TC2, all through ethernet.
I can see how getting 1 GB across this way will be monumentally slow.
However there are these lovely little USB ports on both Time Capsules. Is there a way for me to get the Time Capsule to copy the data from its internal hard drive to a USB external drive? And then vice versa on the other Time Capsule, connecting to it the USB drive with the data from the first Time Capsule?
A related question here might cover one direction, but not the other? And only then if I can find an old version of Airport and the function is still supported by the old Time Capsule with upgraded software.
I am trying the wired ethernet approach, and I see this when copying one of the sparsebundles:
That is with everything wired, and airport on the laptop and the old Time Capsule turned off. I am sharing the old Time Capsule hard drive on the WAN, which is wired to the new Time Capsule LAN. That laptop is on the new Time Capsule LAN.
The wired transfer ended up running at about 48 Mb/s or 6 MB/s. The reason is that the USB-Ethernet dongle I used only supports 10/100 Base-T. No GigE. 48+48 maxed out the 100.
When I went to a Thunderbolt-GigE dongle, the rate went up, but only to 106 Mb/s (13.3 MB/s). The drive in the new Time Capsule can average 1200 Mb/s (150 MB/s) writing. The drive in the old Time Capsule can average 400 Mb/s (50 MB/s) reading. So the GigE is still well shy of what I might expect from USB3, or even USB2.