Be slightly cautious when trying to parallelise disk IO. You can end up with some rather unexpected consequences. You can't change the laws of physics - a rotating platter and moving head still has to move to find data.
So if you start reading from mulitple points on the disk at once, you will create contention and slow down the overall result because of the seek time overhead. You will also make it harder for your OS to predict and prefetch data into cache, which can also reduce performance. Depends on what other workloads and limiting factors are present though - typically the storage subsystem is one of the slowest in your computer system
