> File system metadata structures in HFS+ have global locks. Only one process can update the file system at a time.

Holy heck! How does that work in practice? Do operations get queued and then a single kernel process who can take the lock do the atomic updates?

I have to imagine that is going to cause a bottleneck however, as all non-read operations need to update the metadata (e.g. timestamp, maybe size if it is stored).

That all being said I haven't noticed OS X being particularly slower to do things than e.g. Windows. So if that is the case they're hiding it well.