I am holding 2 hard drive magnets in my hand right now.
Yes, one I bought at an electronics salvage store for $3, the other one I tore out of a dead drive myself. They are both crescent shaped. The magnet itself is rather thin, but the mounting plate it is bonded to is about 1/8 of an inch thick and the overall size is nearly twice that of the magnet.
Each magnet assembly is about 2 inches long and 1 inch wide, slightly curved in an arch, crescent shaped.
The newer hard drives I have been into do have smaller magnets, usually 2 bonded to the mount plate or 2 individually. In a pair, they still trip the sensors in the road.
If neccessary, I can provide photos of what I am describing.
Here is a video of a guy that has made a generator out of a bunch of them. The exact magnets I am describing.
YouTube - Home built electricity magnet generator alternator turbine hard drives
Here's more:
YouTube - Removing rare earth magnet from hard drive backing plate
Here's how to harvest the magnets:
YouTube - super hard drive magnets