Additionally, the FileIO documentation states the following:

    The read() (when called with a positive argument), readinto() and 
    write() methods on this class will only make one system call.

The Linux man page for write() in turn states this:

    On Linux, write() (and similar system calls) will transfer at most 
    0x7ffff000 (2,147,479,552) bytes, returning the number of bytes 
    actually transferred.  (This is true on both 32-bit and 64-bit 
    systems.)