Via the MySQL performance blog: the Percona 2009 conference posted the slides (most of them anyways). There is some very good and diverse material in there (not necessarily MySQL specific). I also found the following link in one of the presentations: http://omniti.com/does/postgresql – love it!
Testing Disk Speed: the dd Test – I/O is the bottleneck in a well-designed DB, so it is important to know how far you can stretch. Along the same lines of database testing we have Database Test 2, a series of test. There are some interesting benchmarks related to different configuration options with different filesystems. Of course, you should do your own testing, but this is a good starting point.
Finally, there are some issues with iotop, but it still helped be in tracking down the fact that when I upgraded to Ubuntu Jaunty (9.04), the indexer got reactivated and it was stressing the harddrive of my machine.
Picture taken from LindaH's photostream with permission.