CompTIA A+ Core 2
Drive wiping vs degaussing vs shredding for A+ Core 2
Match the method to what happens to the drive next. A drive being reused is wiped, which leaves it working. A drive being thrown away, or one that has failed, is physically destroyed, for example by incinerating or shredding it. Drilling a hole leaves parts of the platters readable, and degaussing does nothing to an SSD.
Clear, purge and destroy
NIST SP 800-88 defines three sanitization methods. Clear uses the device's normal read and write commands, for example overwriting all user-addressable space, and protects against simple, non-invasive recovery. It normally leaves the drive usable.
Purge makes recovery infeasible even with state-of-the-art laboratory techniques while leaving the drive potentially reusable. Techniques include the device's dedicated sanitize commands (overwrite, block erase) and cryptographic erase. NIST says purge should be used instead of clear when possible.
Destroy makes recovery infeasible with laboratory techniques and leaves the drive unable to store data again.
Reuse decides the method
Logical techniques such as overwriting are meant to leave the media in a usable state. Physical techniques usually leave it unusable. So drives moving to other employees' workstations are wiped, not shredded.
If a drive will not be reused, NIST says the simplest and most cost-effective method can be to destroy it.
Destruction may be the only option when the drive has failed or is obsolete, because overwriting cannot reach a drive that no longer works.
Destroy techniques and their limits
NIST lists disintegrate, incinerate (burn to ash), melt, pulverize (crush to powder or dust) and shred (cut or tear into small particles).
Bending, cutting, or drilling a hole through a drive may only partly damage it and leave parts readable with laboratory techniques.
As data density and material hardness increase, some techniques become less effective. NIST says pulverize and shred should be avoided for anything but the lowest security categories of data.
Worked example: a failed SSD that held patient records cannot be overwritten, and shredding is not advised for data that sensitive, so incineration fits.
Degaussing, SSDs and certificates
Degaussing was used to purge magnetic tapes and hard disks. It should not be used on non-magnetic media such as SSDs. NIST notes a degaussing run on an SSD can complete successfully yet sanitize nothing. Many degaussers are also too weak for modern high-coercivity drives, and NIST does not count degaussing as an approved destroy technique.
On SSDs, old multi-pass overwrite habits give very little protection because spare cells and wear levelling keep data out of reach of normal writes. Use the drive's sanitize commands or cryptographic erase instead.
After sanitization, complete a certificate of sanitization for each drive. It records items such as manufacturer, model, serial number, the method and technique used, the tool and version, and who verified the result.
Where the exam catches people
- Believing drilling a hole destroys a drive: NIST says it may only partly damage the drive and leave data recoverable in a lab.
- Believing degaussing sanitizes an SSD: degaussing is for magnetic media, and on an SSD it can finish without sanitizing anything.
- Believing wiping is the cheapest choice for drives being discarded: if the drive will not be reused, destroying it can be the simplest and most cost-effective option.
- Believing reused drives must be shredded to be safe: wiping (overwriting) removes the data and leaves the drive usable.
- Believing a failed drive can still be wiped first: overwriting cannot work on a drive damaged to the point of being inoperable, so destruction is used.