With modern drives, the problem isn't that you can recover data from "under" an overwrite. The problem is that hard drives have reserved sectors that are only visible to the drive controller itself, used as spare space in case of a bad sector elsewhere on the disk. (SSDs are even worse since they spread data across the "extra" space all the time, to extend the life of the drive.)
The only way to tell the drive to erase everything is to send the ATA Secure Erase command. This tells the controller to wipe the drive in a secure way. It is the only NIST-approved way to securely erase a drive. Lots of info from this discussion http://security.stackexchange.com/questions/5749/how-can-i-r...
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With modern drives, the problem isn't that you can recover data from "under" an overwrite. The problem is that hard drives have reserved sectors that are only visible to the drive controller itself, used as spare space in case of a bad sector elsewhere on the disk. (SSDs are even worse since they spread data across the "extra" space all the time, to extend the life of the drive.)
The only way to tell the drive to erase everything is to send the ATA Secure Erase command. This tells the controller to wipe the drive in a secure way. It is the only NIST-approved way to securely erase a drive. Lots of info from this discussion http://security.stackexchange.com/questions/5749/how-can-i-r...