I wrote a tool a short bit ago to handle massive parallel hashing. Originally, it was a testbed for a project I built to make multiprocessing easier in Go.

https://github.com/indrora/hyperhash

In it, I learned that there's some interesting quirks about the way the traditional shaXsum tools work, specifically that they focus on a set of inputs from the shell command line, which means that you can exhaust the shell command line length fairly easily (try hashing every file in the Linux source tree, for instance; zsh, bash, and fish will all eventually tell you "Fuck off, there's too many characters in argv")

I also discovered that Go's handling of file handles varies drastically based on OS. Windows, for instance, has no problem with you taking a file handle to every single file on a disk. Linux will get upset but eventually capitulate, macos will stomp its feet and inform you that you are a bad child and kill you off.