Various reasons lead people to recover an old hard drive that has been sitting unused for a long time. When well preserved, an old drive can be sold or given away for future reuse. In order to resell or give away an old hard drive with complete peace of mind, it is essential to make sure it no longer contains the slightest trace of sensitive personal data. A simple deletion is not enough. Indeed, emptying the recycle bin is not sufficient to permanently remove a file on a laptop. On the contrary, this can prove dangerous, especially if the drive contained old sensitive files. Suitable techniques exist that allow you to permanently erase data stored on a hard drive. How is a drive organized and how are files stored on it? How can you permanently erase information stored on a drive?
A reminder on how a drive is organized
A hard drive, whatever its technology, is simply a set of memory cells, each with a precise address. The various files created are stored in these cells and are accessible via their unique address. When you delete a file from the drive, it is not actually erased. Only its reference is removed. In other words, the file continues to exist on the storage medium, but is pending replacement. By deleting it, you are simply telling the machine that the space occupied by that file can be used to host new files. When this happens, the new files overwrite the old ones and take their place. This is the same process that occurs during a high-level format.
As a reminder, high-level formatting is the standard format available on most machines. It is available in the advanced drive options on Windows and MacOS. This type of data erasure is not reliable at all. Although the files appear to have disappeared, they remain accessible using advanced recovery techniques and recovery software. Malicious or overly curious individuals can exploit these gaps to harm you or retrieve sensitive information about you.
At ChronoDisk, we help you recover your files when you accidentally delete them or format a drive by mistake.
How to permanently erase a hard drive?
As you will have understood, a hard drive that has already been used, even after multiple erasures, still contains information. This is due to the particular construction of these drives. Indeed, the memory cells mentioned above are covered with a magnetic layer necessary for storing information. Each of these cells has a magnetic field that is read digitally during read or write operations. It is mainly because of these magnetic fields that hard drives are kept away from magnets. Indeed, a powerful magnetic field created by a magnet or an electromagnet can seriously damage the drive, corrupt the data it contains, and render it unusable.
But there is no need to go to such extremes. As a reminder, our goal here is to resell or give away our old drive after permanently deleting the files. It should therefore be kept in optimal working condition. To do this, techniques exist that make use of various software or utilities depending on the environment and the type of drive.
Using specialized software
If you want to permanently erase old files on a drive or a USB flash drive, the best option is to use suitable software such as Eraser. Since data does not disappear despite being deleted, this software writes random data over your old files. In other words, this software replaces your old files with random files containing no information. On Windows and MacOS, the procedure is as follows:
- download and install software suited to your environment for performing permanent deletion tasks;
- configure the various permanent deletion options (quick, slow, advanced, etc.);
- perform the permanent deletion operations on the relevant drives;
- make sure to clean each disk partition for partitioned drives.
Permanent deletion options vary depending on the software used. With the Eraser software, for example, the Gutmann deletion method rewrites over your old data 35 times. This makes any recovery attempt impossible with ordinary equipment.
Linux environment
To permanently erase a drive under GNU/Linux, you need to use the terminal. By replacing “/dev/sdX” with the target hard drive, the command dd if=/dev/urandom of=/dev/sdX bs=8b conv=notrunc permanently deletes data in a Linux environment.
Low-level formatting
Low-level formatting is a hard drive repair and initialization tool. It is only accessible through specific utilities and through the manufacturer. This type of formatting completely restructures the drive, as if it were fresh out of the factory.