I am just not sure what direction the files are moving in.. or what the second drive is.
Do you mean you have a Time Capsule which has internal drive.. and you are copying the files from LaCie USB drive to the Time Capsule internal drive??
If I have it wrong.. what or where is the second drive.
I will assume the copy is USB to TC internal drive.
USB port on all Time Capsules / Airport Extreme are USB 2.0 but they are hampered by slow processors. Speed is woeful.
If you are using wireless instead of ethernet that makes it double bad... because all packets go from USB to Computer over wireless.. computer back to the TC over wireless.. and then written to the internal hard disk.
Wireless being half-duplex makes this hugely slow.
There are two major speed ups.
- Plug the USB into the computer. If it has USB3 interface all the better.. even FW800 beats USB2.
- Use ethernet.. if at all possible.. even to buying a thunderbolt to ethernet dongle that matches the age of the computer.