Reading remapped hdd sectors

Question

I am testing secure-erase-enhanced in hdparm. I want to examine the spare sectors to check that there is no sensitive information remaining. How can I access the remapped sectors to read their contents?

Answer 1

The physical sectors on the HDD gets remapped if there is non-recoverable ECC error.
There is no need to examine the unused spare sectors, since they will be empty and the ones which are used are mapped instead of the original sector.

The original sector is not available to the OS (the remapping is transparent to the OS) so you won't be able to write to it or read from it. You could try to do low level formatting, but that still doesn't guarantee that you will be able to access the corrupted sector to overwrite them. Also low level formatting might not be available for your HDD model.

If you want to make sure that nobody will be able to read any information from the corrupted sectors you would have to physically damage the platter in that place.
In most cases that's an overkill for the following reasons:

• the original sectors are corrupted, so the data extraction/recovery will be extremely difficult.
• the data extraction/recovery would require special equipment
• the data extraction/recovery would be very specific for that particular model of HDD
• the original sectors will be scattered so even if the data recovery will be successful there won't be any context to figure out what the data mean (because you already did secure erase for the rest of the disk)