After jailbreaking each of my Time Capsules, I wanted to transfer a pair of .backupbundle files, but they refused to transfer via Finder, so much for drag and drop compatibility. Just as well, there’s a secure way to do it via Terminal.app using these instructions:

1. In macOS, mount a disk from each Time Capsule drive you’d like to pass information between.
2. Open Terminal.app.
3a. To transfer data from your Time Capsule to a drive mounted locally, execute this command from your Mac:

scp -3 -r root@10.0.1.15:/Volumes/dk2/ShareRoot/tina.backupbundle /Volumes/WD\ 4GB\ Backup

3b. To transfer data between a pair of Time Capsules, this command should work:

scp -3 -r root@10.0.1.15:/Volumes/dk2/ShareRoot/tina.backupbundle root@10.0.1.1:/Volumes/dk2/ShareRoot

4. You can continue to monitor the status of the transfer in the Terminal.app window, this will likely take several hours if the .backupbundle file is more than a terabyte.

If you are doing this transfer, you too may be like me and finding your internal Time Capsule drive out of space. If you make a secure shell connection to your Time Capsule, you can execute the following command to find out how much space remains on the Time Capsules internal storage and disk drive:

df -h

Filesystem Size Used Avail %Cap Mounted on
/dev/md0a 15M 11M 4.5M 70% /
/dev/flash2a 2.7M 63K 2.5M 2% /mnt/Flash
tmpfs 16M 4.0K 16M 0% /mnt/Memory
/dev/dk2 2.7T 2.0T 746G 73% /Volumes/dk2

In the case above, only 0.7 TB remained on the storage disk and I needed a bit more to fit everyone in the family…