In Linux, it simple to change a hard drives I/O scheduler.  Why would you want to do this?  Simple, performance.  Some file systems work better with a scheduler other than the default.
To set a hard drives I/O scheduler.

echo "schedular_name" > /sys/block/<drive>/queue/scheduler

For example:

# echo "deadline" > /sys/block/sdc/queue/scheduler
# cat /sys/block/sdc/queue/scheduler
noop anticipatory [deadline] cfq