Securely erasing SSDs: why multiple overwriting is not enough - and which methods really work
Why overwriting reaches its limits with SSDs
With conventional hard disk drives (HDDs), multiple overwriting was long considered a reliable way to destroy data. The logic was simple: if you write new patterns to every location on the disk several times, you inevitably overwrite the old contents in the same physical location.
With SSDs, this assumption no longer holds. Solid state drives use wear levelling, an internal management system that distributes write operations evenly across all memory cells to extend their service life. In doing so, the controller decouples the logical address seen by the operating system from the actual physical cell. A supposed overwrite therefore often ends up in a completely different location - while the original data remains untouched in reserve areas.
In addition, every SSD has extra capacity that cannot be addressed directly from outside at all. Data remnants can hide in this so-called over-provisioning area, where an ordinary overwriting tool will never reach them.
ATA Secure Erase and Crypto Erase
Rather than writing patterns from outside, effective methods work through the SSD's own controller. ATA Secure Erase is a command built into the drive that resets all memory cells, including the hidden reserve areas, in one go. Because the controller carries this out internally, it also reaches the areas that wear levelling would otherwise put out of reach.
Crypto Erase is even faster. Modern SSDs encrypt their data by default with an internal key. With Crypto Erase, this key is destroyed and a new one generated. The data is then still physically present, but without the matching key it is nothing more than unusable gibberish - recovery is practically impossible.
Both methods are clearly superior to conventional overwriting methods for SSDs, because they take the characteristics of flash technology into account rather than ignoring them.
Certified tools and documented proof
In practice, it is not enough for businesses that an erasure has taken place - it must also be provable. Certified tools automatically select the right method for each drive, verify the result and generate an audit-proof erasure log.
Such proof is particularly important when storage media leave the premises, for example when they are sold, when leased devices are returned, or in the context of compliance requirements and data protection. A documented erasure process provides assurance for customers, auditors and supervisory authorities.
Secure SSD erasure with TechResellers
At TechResellers, certified data erasure is an integral part of our refurbishment process. We use the methods suited to SSDs and, on request, issue a traceable erasure log for every device.
This means Swiss businesses and private buyers can pass on their decommissioned hardware with peace of mind - and anyone who buys a refurbished device from us receives storage that has been reliably and thoroughly cleared of all previous data. Get in touch if you would like to retire your IT hardware securely and in an environmentally conscious way.