Interesting. We use it to mmap a big file that just-enough fits in memory and we mostly read randomly (around 1/1000 of the file) and sometimes sparringly write and it works great. I haven't tested how would it work more fast with Seek/Read/Write, but mmap is very ergonomic for this; it just acts as a slice and it's basically invisible; and you can then take the slice of bytes and unsafe.cast it as slice of something else. Very easy.