nix copy --to ssh://<host> <path> and I got the following progress line (snapshot after several minutes of running):
[8/198/789 copied (745.7/4080.7 MiB)] copying path '/nix/store/11jrlrjdq0bhx0kqmb6810zgyf12jcn8-attoparsec-0.13.2.2-doc' to 'ssh://<host>'
8/198/789 is not really a clear format. The only related info I found in the manual is:
It is much less verbose. By default, it displays a single-line progress indicator that shows how many packages are left to be built or downloaded,
which doesn’t really clarify anything
The value for total size of closure (
4080.7 MiB in above output) increases as the upload proceeds (at first it showed a value of ~1GiB for several minutes).
In it unclear to me why this would be the case when
nix path-info -S <path> will instantaneously return the total size.