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Wear Leveling
In brief
Wear leveling (in German: Verschleißausgleich) is a method in SSDs, USB sticks and memory cards that distributes write operations evenly across all flash memory cells. Because each cell can only withstand a limited number of write cycles, this extends the life of the data carrier. For data erasure it means: when a file is overwritten, the new data ends up in a different place, and the old data may be retained.
How wear leveling works
A controller in the data carrier translates the operating system's logical addresses into physical storage locations. This mapping is called the Flash Translation Layer. When a file is changed, the controller writes the new data into free blocks and marks the old ones as invalid. Only later does it clean them up.
| Variant | Principle |
|---|---|
| Dynamic wear leveling | New write operations preferably go to little-used free blocks |
| Static wear leveling | Even rarely changed data is occasionally moved so that all cells age equally |
This is supported by Over-provisioning, a memory reserve invisible to the user, and by the command TRIMwith which the operating system reports deleted areas.
Consequences for data erasure
Because of wear leveling, overwriting from the outside is unreliable on SSDs: the software sees only logical addresses, not the physical cells. Reserve blocks and retired cells remain untouched. Methods that the controller itself executes are safe, such as Sanitize commands or Crypto Erase. More on this in the guide Securely erasing hard drives and SSDs.
Second IT erases SSDs with Blancco and issues a digitally signed erasure certificate for each device. More on certified data deletion.
Frequently asked questions about wear leveling
Can wear leveling be turned off?
No. It is an integral part of the controller firmware and necessary for the SSD's service life.
Is repeated overwriting enough on SSDs?
Not reliably. Even multiple passes do not reliably reach all physical cells. Firmware commands or crypto erase are the better choice.
Does wear leveling also affect USB sticks?
Yes, most flash memory uses it. Because erase commands are often missing there, USB sticks are frequently destroyed physically.
What is the difference between dynamic and static wear leveling?
With dynamic wear leveling, new write operations preferably go to little-used free blocks. With static wear leveling, even rarely changed data is occasionally moved so that all cells age evenly.
How do I securely erase an SSD despite wear leveling?
With methods that the controller itself executes, such as Sanitize commands or crypto erase. They act on the physical cells, not just on logical addresses. A report per drive documents the result.
Securely erase SSDs – with the right method and proof.
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