It appears large writes (greater than 32bit) are getting truncated to values near (but not at) the largest value representable in 32bits. Specifically, for both @saghul and I, the output ends up being 2147479552 bytes for a 1000_1000_1000*4 byte write. For reference, INT_MAX on my system is 2147483647L; thus the write creates a file exactly 4095 bytes shy of INT_MAX.

The gist at:

https://gist.github.com/tfogal/9765258

adds a new test that fails for both @saghul and I.

@saghul suspects that the write is getting interrupted and libuv isn't properly restarting it.