Let us talk about Wiping a Disk Once – Enough to Securely Get Rid of Data. Unlike to most popular disk cleaning legends that say that you need to overwrite a drive multiple times to make the data unrecoverable, the truth is that you only need wipe a drive once. ‘Wiping’ actually means overwriting the drive with all 0’s or 1’s. it is recommended that the drive be wiped once before disposal so that the data becomes unrecoverable, but wiping multiple times is just of no use.
What happens when you ‘Wipe’
On deleting a file from your operating system, the OS marks the sectors containing the data as ‘Unused’, rather than removing all traces of the file from the hard drive. These ‘Unused’ sectors can be used to write data later. However, if these sectors haven’t been overwritten already, you can use the File Recovery utility to recover data from these sectors. To delete a file completely, it would take the OS additional resources. A file can be marked ‘Unused’ very quickly but to write over it would take much longer. Writing over the sector or overwriting over the sector takes the same time and resources, so it is preferred to not delete and write. By ‘Wiping’ a drive, you overwrite all the data with 1’s or 0’s or with a random combination of 1’s and 0’s.
Difference between Hard Disk Drives and Solid State Drives
The traditional way of wiping data applies to Hard Disk Drives. It is a lot different in case of the Solid State Drives. On an SSD, if an OS deletes a file from the SSD, it sends a TRIM command to it and the drive erases the data. Overwriting takes much longer than writing on an unused sector on an SSD, hence, it is preferred to erase the sector, for increased performance of the SSD. Also, an SSD should never be ‘Wiped’, deleting files form it is enough. Since SSDs have limited write cycles, wiping them would just eat up write cycles and not be productive in any way. It also means that File Recovery tools would not work on an SSD.
The Legend of Wiping
Since on the Hard Disk Drives, data is stored magnetically, it has led people to theorize that it is possible to examine a sectors’ magnetic field with a Magnetic Force Telescope and determine the sectors’ previous state even after it has been overwritten. As an extension of the same theory, people also suggest that a data be written to the sectors multiple times to ensure its non-deletion. There are tools available with built-in settings to perform up to 35 write passes, known as ‘Gutmann method’, taken after Peter Gutmann who wrote a well-known paper on the subject published in 1996, ‘Secure deletion of data from Magnetic and Solid State Memory’. The fact is that the paper was a lot misinterpreted and became the source of the 35 pass urban legend.
What the reality is
It isn’t necessary to follow the Gutmann method because the paper was published in 1996, when the older hard drive technology was in use. It was written and the Gutmann method was designed in general for modern Hard Drives to the ancient ones. Guttmann himself explained, in an epilogue written later, that for a modern drive, one or at most two Wipes is sufficient.
The modern drives have more data packed into decreasingly smaller areas and hence, theoretical data recovery is essentially impossible. We can say that disk density is an important factor. Also, the use of Magnetic Force Microscope to recover data has never been implemented practically; hence it remains completely theoretical and limited to older hard disk technology.
Alternatives to Wiping
If you are unsure about the one-Wipe-is-enough, you can try out something else. You can use a Degausser to eliminate the drives magnetic field, but this may destroy some drives. You can also physically destroy your hard disk, which is a real big deal!