""" Modern HDDs present a consistent interface to the rest of the computer, no matter what data encoding scheme is used internally. Typically a DSP in the electronics inside the HDD takes the raw analog voltages from the read head and uses PRML and Reed–Solomon error correction[144] to decode the sector boundaries and sector data, then sends that data out the standard interface. That DSP also watches the error rate detected by error detection and correction, and performs bad sector remapping, data collection for Self-Monitoring, Analysis, and Reporting Technology, and other internal tasks. """
With the answer I gave above, and the fact that it's already being done in hardware, I don't think adding another layer of EC will be fruitful.
[1] https://en.wikipedia.org/wiki/Hard_disk_drive#Access_and_int...