Postmark is a benchmark, which test performance of reading and writing to multiple files.

Download the c file and compile it. When running the program you will get a command prompt. From there you can run a few commands to customize the test. By typing help you will get a list of all possible commands. With run you will start the performance test. If you didn't set any options, it will run with default options.

A possible output could look like this:

pm>run
Creating files...Done
Performing transactions..........Done
Deleting files...Done
Time:
        158 seconds total
        66 seconds of transactions (7 per second)

Files:
        760 created (4 per second)
                Creation alone: 500 files (5 per second)
                Mixed with transactions: 260 files (3 per second)
        224 read (3 per second)
        0 appended (0 per second)
        760 deleted (4 per second)
                Deletion alone: 520 files (86 per second)
                Mixed with transactions: 240 files (3 per second)

Data:
        3584.00 megabytes read (22.68 megabytes per second)
        12160.00 megabytes written (76.96 megabytes per second)
pm>quit