Why Your SFTP Transfer Is Stuck at 2 MB/s (and...

Two minutes to copy a 274 MB file to a VM running on localhost. Not over the internet. Not to a cloud instance across the country. Localhost. The same machine, loopback, zero network latency. That was the experience a user reported in issue #290 on cubic, a lightweight CLI for managing QEMU/KVM virtual machines. The maintainer reproduced it, traced the problem to the upstream russh-sftp crate, and posted a comment asking if anyone had ideas about where the bottleneck was. I did. The answer turne