Microbenchmark that executes 1000 single-byte writes.

bench.c

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>
int main() {
    int fd = open("bench.dat", O_WRONLY|O_CREAT|O_TRUNC, 0666);
    if (fd < 0) {
        fprintf(stderr, "open failed: %s\n", strerror(errno));
        exit(1);
    }
    int r = posix_fallocate(fd, 0, 1000);
    if (r != 0) {
        fprintf(stderr, "fallocate failed: %s\n", strerror(r));
        exit(1);
    }
    r = fsync(fd);
    if (r != 0) {
        fprintf(stderr, "fsync failed: %s\n", strerror(errno));
        exit(1);
    }
    int i;
    for (i = 0; i < 1000; ++i) {
        r = write(fd, "a", 1);
        if (r != 1) {
            fprintf(stderr, "write failed: %s\n", strerror(errno));
            exit(1);
        }
        r = fdatasync(fd);
        if (r != 0) {
            fprintf(stderr, "fdatasync failed: %s\n", strerror(errno));
            exit(1);
        }
    }
    return 0;
}