Measuring disk I/O speed

Disk thruput tester is a handy tool to test the sequential read and write performance of storage media, like harddisks and SSD. It supports configurating custom block sizes:

http://www.objectso.nl/

Using this tool, testing the read/write performance of 8KB, 16KB, 32KB, etc, sized blocks is a breeze. The size and location of the test file is also configurable.

Note: on the website the tool is called "disk throughput tester".