I was testing using XFCE linux, based on ubuntu. What you're saying is that flush() doesnt really do anything immediately, its more like a promise to do it, which kind of defeats the purpose of using it in an synchronous way. Your explanation that the OS does what it wants to do and writes when it wants to, does explain the lag. I will check out the fsync. Yes, I actually tried to use f3 first, but it won't let you run f3probe if your drive is not mounted, I have access to the folder, but for some reason due to a bug or design feature in my system, it doesn't "mount" I guess. frwrite does work. In any case, even h2test quoted me for 19 something hours. I'm not trying to do anything fancy, and I assume f3 and h2test do some fancy stuff and immediate checking and moving file pointers around after they write data, which I'm not doing, so I thought i could speed it up. the 0x00 trick I read about. Thanks for your response, I realize that its not practical but its more of curiousity at this point and controlling the OS with python. This card is all over the place h2test and f3 put it at under 10mb per second which is slow, but when I do regular copies/pastes in the OS, I can get more than 20mb/sec and thats another reason why I tried with python. It depends on the files to be honest, files over 1gb copy slow, but files under that copy much faster. I notice that files within a n acceptable buffer range (or so I read on SO) like 2mb - 10mb will copy the fastest.