When it comes to figuring out how a file system behaves on a HDD or SSD I generally first turn to Bonnie++ as a straight forward and easy to use disk benchmarking tool.
Bonnie performs a series of tests, covering character and block read/write I/O, database style I/O operations as well as tests for multiple file creation/deletion and some random access I/O operations.
To install bonnie for Ubuntu, simply do:
sudo apt-get install bonnie
To get a fair I/O benchmark (without the memory cache interfering with results) Bonnie generates test files that are at least twice the size of the memory of your machine. This can be a problem if you have servers with a lot of memory as the generated files can be huge and testing can therefore take quite a while. I generally boot a system and specify ~1GB of memory using the mem=1024M kernel parameter just so that Bonnie only tests with a 2GB file to speed my testing up.
My rule of thumb is to run Bonnie at least 3 times and take an average of the results. If you see a large variation in your results double check that there isn't some service running that is interfering with the benchmarking.
Bonnie references:
http://www.coker.com.au/bonnie++
http://linux.com/archive/feature/139742
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