From Barefeats:
DISKTESTER 2.0
Lloyd Chambers has released version 2.0 of his useful
DiskTester utility. Though it runs from within the Terminal app, we like the flexibility of defining the size of the test file, the size of the transfer or 'chunk,' and the area of the volume to be tested. We often use it to simulate a full volume.
http://www.barefeats.com/hard76.html
You may remember Lloyd from the days of AutoDoubler and CopyDoubler (I think that was the name). Long time Mac developer.
Mac Pro 2GHz 2GB WD Raptor/Caviar RE 320 Mac OS X (10.4.7)