I haven't tried it on crazy amounts of files, but it's just using node's basic async I/O under the covers, and reading once. If you notice any sluggishness let me know!

It's also greatly impacted by what plugins choose to do. I had an extra clone call (literally cloning the buffers for each file) in the templating plugin at one point that like 50x'd the build time :) Everything I've done so far though has sub-second build times—quick enough that I've been building on every request[1] in development which makes things super simple.

[1]: https://github.com/segmentio/metalsmith.io/blob/master/serve...