Back in the 1990s, a standard for the destruction of sensitive data was created by the Department of Defense for hard drive and media being disposed of by the government’s defense and security agencies. Coined the “DoD wipe”, the process involved a 3-pass over-write procedure that would effectively erase data from a hard drive. At the time there were no other standards – government or industry – so most enterprises adopted this “DoD wipe” as their own policy. Even to this day, many companies will insist on this “DoD wipe” or “3-pass”, despite it being obsolete as a government standard. The current reference standard is the NIST 800-88, Rev 1 document (which was updated in 2012 and adopted in 2014).
At the point of publication, the DoD wipe procedure made a lot of sense. But now there’s little reason for the 3-pass wipe. Compared to 20 years ago, we have better hard drive technology and erasure software, and documented processes to ensure the erasure is successful.
Why a 3-pass Procedure Was Chosen
So why were three passes the magical number for erasure of data? Why not two or four or ten? Quite simply, it was thought that three was a good number. There was no testing that demonstrated three passes would be more effective than two or less effective than four. Based on the then-current hard drive technology, more than one pass was believed to be needed because of the precision of the write head and the way the firmware read and wrote to each sector. One pass might not get every sector overwritten, every time. A number was chosen that satisfied the needs of the Department of Defense.
Improvements in Drive Technology
When the DoD standard was adopted, technology was not nearly as advanced as it is now. In the 1990s, data sanitization practices were developed for slow magnetic hard drives with capacities less than 1 megabyte, and it was shown that a series of three manual passes would be sufficient. What may confuse some non-IT professionals is why a single pass would now be as effective as three passes, based on the fact that hard drives have a much greater capacity. The reason for this is that two types of technology have advanced since the DoD standard was created. The first involves the technology of the hard drives that are in use. Today’s drives are much more precise than older magnetic drives, which means that the head will write over every sector reliably with just one pass. The second improvement in technology comes from the software tools that have been created to assist in the procedure. Software tested and certified such as that from Tabernus or Blanco enable verifiable overwrites with detailed records.
Risk vs. Cost
It’s a given that the less work that needs to be done, the lower the cost will be. A 3-pass procedure takes, you guessed it, three times as long as a single pass. This is significant with higher density drives. A 1Tb drive can take hours to fully wipe once (time varies depending on the drive interface, and the systems being used). Additional costs to do additional overwrite passes only increases processing costs and does not technically reduce risk.
Number of Passes vs Process
There is at least as much risk in the process for data destruction as there is in the technical erasure process. In this case, the process includes how you store, track and ship hard drives from the time you retire them until you dispose of them, what procedures your ITAD vendor has in place to ensure and document data destruction and also the quality assurance procedures.
Of course, if your company policy insists on 3-pass (or any number higher than 1) the software tools can be set to automatically perform the multiple passes and record the results. You should consult with a Data Destruction expert to determine the best options for your company. A NAID AAA certified company will have the expertise and the processes in place to ensure the security of your data.
