"Jacob Read" <23*7*9*6@s*u*e*t*u*a*e*u*a*> wrote: I believe the problem reporting negative I/O times has been corrected. Please report any problems. The arithmetic was being performed using a standard int (4 bytes), which overflowed with larger (faster) I/O speeds. If you're having similar problems, you can perform the arithmetic using int64_t or double. You may like to read about the ceil() function, too.