An exception does not mean a failed wipe, rather the wipe has overwritten every logically available sector, but not every physical sector on the drive.

This occurs when 

  • Remapped sectors have been discovered during the erasure
  • The software could not remove a:
    • Host Protected Area(HPA) or
    • Device Configuration Overlay (DCO)

 

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. There is the potential that user data will remain in the original physical sector that may be forensically recovered at a later date.

Remapped Sectors are discovered by Tabernus erasure software and reported, and will cause the ‘exception’ (this is not the same as a ‘failed’ wipe).

 

Host Protected Area (HPA) 


Tabernus software can detect Host Protected Areas and erase them. The HPA is commonly used to store the recovery part of the operating system and can contain sensitive data. When a Host Protected Area is found the area is erased as a default. A dialog box will be shown if a problem occurs with this erasure. For example, in some cases the computer must be rebooted in order to remove the HPA. In certain circumstances, it may not be possible for Tabernus to remove an HPA, the user will be warned of this prior to starting the erasure, and the outcome will be an Exception, as there are physical sectors on the drive that cannot be accessed logically. It is possible in these cases to remove the hard drive from the original machine, and erase it in a donor chassis or other hardware known to be able to clear HPAs.

 

Device Configuration Overlay (DCO)

 

Device Configuration Overlay allows system vendors to purchase data storage devices from different manufacturers with potentially different sizes, and then configure all devices to have a specific capacity by trimming the number of logically accessible sectors. This area of the drive, though inaccessible, may contain user data as the DCO size may be changed at any point during the lifetime of the drive. In order to remove this user data Tabernus is automatically configured to detect and remove the DCO area. In certain circumstances, it may not be possible for Tabernus to remove a DCO, the user will be warned of this prior to starting the erasure, and the outcome will be an exception, as there are physical sectors on the drive that cannot be accessed logically. It is possible in these cases to remove the hard drive from the original machine, and erase it in a donor chassis or other hardware known to be able to clear DCOs.


Procedure


In these cases, the user's waste/security policies come into effect: if the drives possibly have very sensitive information on them - and hence possibly on any remapped sector - they would likely shred or degauss the drive. If the data on the drive is not sensitive, many will happily reuse the drive safe in the knowledge that only detailed forensic techniques could retrieve any 'remapped data'.