Thread: My 4K Write Program is nowhere near as fast as benchmarks

  1. #1
    Registered User
    Join Date
    Sep 2011

    My 4K Write Program is nowhere near as fast as benchmarks

    So I wrote this program that writes 100,000 4K .txt files onto disk.

    HD Tune Pro says my 500 MB RAM disk gets ~90k IOPS for 4k files, ~350 MB/sec

    Here is my program:
    #include <iostream>
    #include <fstream>
    #include <cstdio>
    int main() {
        char filename[100];
        for(double o = 1; o<100000; o++)
            std::sprintf(filename, "%05.0lf.txt", o);
            std::ofstream ofs(filename);
            for(int i = 0; i < 77; i++)
                ofs << "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
            ofs << "aaaaaaaaaaaaaaa";
        return 0;
    Which gives me ~400 IOPS on the ramdisk. How can I make this go faster?

    My Ctrl+S addiction gets in the way when using Code Blocks...

  2. #2
    Registered User
    Join Date
    Dec 2011
    Not exactly sure if the same principle applies in C++, but...

    You should probably make a 4k buffer in the beginning, and initialize it to all 'a's. Then in the loop, copy the entire buffer to the file at once.

  3. #3
    Algorithm Dissector iMalc's Avatar
    Join Date
    Dec 2005
    New Zealand
    Apart from what memcpy says, you cant test it that way because creating so many files means lots of reads and writes to and from the directory. As such, I would expect a program such as the above to take more than twice as long as quoted.
    All you're doing is wearing out the disk faster.
    What would make sense for testing write speed would be to append 4096 bytes to a binary file at a time. You would only have the one file.
    You would use the "write" member function.
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