The data copying started yesterday finally wrapped up late this
morning. Using a basic dd invocation to load the NixOS boot
image onto the external 2TB drive I had (I think I picked it up a few
years ago to help tame my data) allowed me to boot off of it on the test
laptop, and so now the next step will be booting with that drive on the
target server. I'll probably also look to rearrange the data on that
server rather than wiping the drive, so resizing or changing the
partitions (or installing another HDD) will probably be another chunk of
time while I also read a bit more of the NixOS user guide.
I've just opted to connect the 1TB drive that I have using the USB connector for now…it probably make sense to mount it internally afterward. The server also offered to boot from the 1TB drive, so that may have been an option all along. For now I'm just clearing off the content of the current server drive onto the 1TB drive which is also taking a fair amount of time and is likely to drag this to tomorrow.