Interesting information on erasing HDDs

The erasure of magnetic storage media is done by physically overwriting all areas of the medium. The decisive factor is that all protected and hidden areas such as HPA, DCO, FAT are recognised and overwritten as well.

The common deleting algorithms differ in two main points:

Type of overwrite

One distinguishes between a fixed pattern and random characters. They are often used in combination.
For example, DOD 5220-22 M with a 3x overwrite:
1st & 2nd round with fixed pattern –
3rd round with random characters

Number of overwrites

Depending on the security needs, the number of overwrites will vary from a 1x (HMG standard low), a 3x (US DOD 5220-22M) to a 35x (Gutmann) overwrite.

The opinions about the type of overwrite and the number are different.
We recommend a 1x overwrite for slightly to medium sensitive data, a 3x overwrite for medium and highly sensitive data.


After the deletion has been completed, the various areas undergo verification. Random sectors are selected and compared. The decisive factor is the conformity of the samples.
By default, 10% of the surface of the corresponding data carrier is checked. In the case of a negative verification, the deletion process is deemed unsuccessful and the data carriers are removed.

DHCS works exclusively with certified deletion software. In this way, we can provide absolute security for overwriting protected and hidden areas, as well as effective physical overwriting of the sectors.