MHDD 4.6 is extremely useful. You can erase slower clusters and bad sectors from the drives geometry without losing any data.
Quote: start hirens, Hard Disk Tools --> More---> More--->MHDD4.6 . Select your drive (by pressing the corresponding number). Then pres F4, activate (with space key) remap (the data from the bad clusters will be moved in good clusters) and then pres F4 again. If your drive it's not severely damaged expect 1-2 hours to finish. When this step is finished press F4 again, activate erase waits (this will erase all slower clusters and bad sectors from drive's geometry) then hit F4 again. Wait to finish!