Spare sectorsas a proportion of LBA size

[pleriche]

Grown defects can result in user data being left in the defective tracks. This it not normally a problem as run-of-the-mill tools can only access LBA sectors. As a result, simple data wiping tools such as DBAN may leave residual data still accessible to specialist or forensic tools.

In order to quantify this risk, I'm interested to find out what proportion of the advertised LBA size of a hard disk is typically set aside as spare sectors, and hence the maximum possible proportion of a user's data might survive a simple wipe in a heavily remapped drive. I'd be grateful if anyone could enlighten me.

I wondered whether I could find out for a specific hard drive using MHDD. Perhaps if I could use it to disable sector remapping I might see the raw disk size, and maybe even turn off the bad sector bit in bad sectors in order to attempt to reread or overwrite them. Is that possible? I don't see it from the docs. That (or something similar) must surely be how forensic tools would read them, and how certified data wiping tools such as Blancco can achieve more than DBAN.

[pleriche]

(I'm sorry, this is a near duplicate of my posting yesterday. Foolishly, I didn't realise posts were moderated and thought I hadn't properly submited my post.)