PyPy is faster than Python, yes. But Go, C and many other (compiled) languages are way faster than PyPy. Plus, if you use a language like Go or Rust then you avoid Python's GIL and you'll have much more reasonable memory usage. Best of all, deploying is a matter of copying a binary, rather than having to deal with the absolute disaster that is Python packaging.

Maybe plenty fast for most applications but a filesystem is not one of these IMHO, especially for something as naturally resource hungry as ZFS.

A good filesystem implementation requires tight memory management and good control of what happens at the OS level. I am not saying it can't be be done in python, but it clearly isn't the right tool for the job.

I meant that for a production implementation. Python is perfectly fine for a proof of concept, in fact, it may be better than jumping straight down to C. But keeping it for production is foolish IMHO.

Faster that CPython doesn't mean it is fast.

I routinely fail to get speedup on PyPy. In fact I frequently get slowdowns. I imagine it's only fast if your code is slower than it needs to be to begin with.

Only when comparing to CPython

pypy is fast, but even were this written in C, there's still the kernel-userland boundary to contend with.