Best Practices for Media Destruction

This document is intended to offer best practices for the destruction of various media types prior to reuse, disposal, or RMA. As they have the highest capacities and the greatest potential for reuse, the focus of this paper is hard disks. The table at the end of this document will cover most common digital media. No practices for file-level destruction are discussed; these practices apply to the complete medium and all its content.

Media destruction, either physical or electronic, is intended to prevent data disclosure. Hard drives returned to vendors as defective are frequently repaired and returned to service with data intact. Disposed functional hard drives are a valuable commodity and present significant risk of data disclosure if not properly treated. Even if the drive is to be reused it should be wiped.

According to DoD 5220.22, functional drives should be overwritten 3 times prior to disposal or reuse. However, according to NIST 800-88, modern hard disks can defy conventional forensic recovery after a single wiping pass. As of 2001, ATA (thought not SCSI) drives support a secure-overwrite command that should eliminate all data on the drive much more rapidly than operating system-level utilities. Our recommendation acknowledges the NIST document but maintains consistency with other practices throughout higher-education and industry. We recommend the use of a reputable wipe utility implementing DoD 5220.22 for drives that will be reused or disposed of in a functional state. Be aware that a 3-pass wipe of a large hard disk is time-intensive. See Table 2.

Drives that are defective, dead, or sufficiently unresponsive that they do not complete the 5220.22 wipe protocol, should be physically destroyed prior to RMA or disposal. The objective of physical destruction is to badly warp or distort the platters, rendering the drive or any of its components inoperable. This can be achieved by drilling the drive in several locations perpendicular to the platters and penetrating clear through from top to bottom. Hammering or crushing is equally effective but more labor intensive. Simply destroying the logic section of the drive without damaging the platters is insufficient and not recommended.

Degaussing modern hard disks requires magnets capable of generating fields several orders of magnitude stronger than those required to blank audio and video tapes. Industrial degaussers rated for hard disks are available but are very expensive. Further, their duty cycle is very short, and may not be suitable for large numbers of drives in a short time. As degaussing destroys hidden portions of the drive used for bad block recovery, drive head positioning, and other functions, drives subject to it will be nonfunctional. For these reasons, physical destruction is the preferred practice.

Degaussing is a suitable practice for other magnetic media such as floppy diskettes and backup tapes. Degaussers for this purpose are typically cheaper and can be operated longer between cooling periods.

A discussion of solid-state media is appropriate. USB drives, compact flash, MMC/SD, and the like are unreliable in the face of disk wiping protocols. Multi-pass wiping is not technically relevant for solid-state devices. More importantly, solid-state storage has a very limited number of read/write cycles and is designed with considerable surplus. This surplus storage is used to relocate data away from failing data segments. Wipe utilities cannot guarantee that all originally allocated blocks have been wiped. Further, they cannot insure new data is properly commited to the device. If disposal is the ultimate goal, physical destruction is strongly recommended.

Table 1: Destruction practice for various media

Table 2: Media destruction services and utilities

DBAN: http://dban.sourceforge.net a bootable floppy/CD utility implementing various full-disk wipe protocols including DoD 5220.22. The DBAN ISO is included in CIT's distribution of Helix: http://helix.cit.cornell.edu Helix includes disk- and file-level wipe utilities

http://www.backthruthefuture.com is a service that will physically destroy hard disks and provide certification of their destruction

http://www.actfirstshredding.com is another service that will physically destroy various media and provide certification

http://www.mandkgroup.com/about.html is another service that will physically destroy then recycle various media

http://www.degaussers.com supplies magnetic media degaussers ranging from handheld types suitable for diskettes or audio tapes to large industrial devices