Best Way to Compare Two Directories
I needed to compare two directories, on two machines, containing 32GB+ of thousands of files. The rsync command was what I needed.
rsync has an -i option: --itemize-changes. What it does is display a summary of all the changes. Coupled with the -n option (--dry-run) and the -r option (--recursive), it allows to efficiently compare directories, possibly over ssh.
The basic command is:
$ rsync -rin -e ssh /path/to/local/dir/ remote:/path/to/remote/dir/
The output is somewhat cryptic, but all is cleary explained in rsync’s manpage.