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