What are remapped sectors?

When a sector on a disk is found to be ‘bad’ or unstable by the firmware of a disk controller, the disk controller remaps the logical sector to a different physical sector. Typically, automatic remapping of sectors only happens when a sector is written to.

Essentially, if disk drive firmware (or disk controller error detection/correction code) detects that a sector is exhibiting excessive errors during reads or writes, that sector is 'hidden' and remapped to another sector from a batch kept spare for this specific reason. The drive (and therefore user, host, and application) then has no way of accessing the original sector(s). However, if data was written to the sector prior to remapping of the sector, there is the possibility that this data will remain in the original physical sector and may be forensically recovered.

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