Why isn't overwriting a file with zeros a reliable way to erase it from an SSD?
Old copies can stay in flash pages the drive no longer maps.
- NAND flash cannot store zero bits
- TRIM changes written zeros back to old data
- Old copies can remain in unmapped flash ✔
Why: An SSD maps logical addresses onto changing physical flash pages. An ordinary rewrite need not reach every physical page that held the old data. NIST recommends media-specific sanitize methods that bypass normal read and write abstractions.
Huh, didn't know that: NIST says cryptographic erase can rapidly sanitize data, but only when its encryption and key-handling conditions are met.
Why can't SSDs keep secrets? They never really let go of the past.
References
Answer: Old copies can remain in unmapped flash. An SSD maps logical addresses onto changing physical flash pages. An ordinary rewrite need not reach every physical page that held the old data. NIST recommends media-specific sanitize methods that bypass normal read and write abstractions.
- NIST SP 800-88 Rev. 2: Guidelines for Media Sanitization nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-88r2.pdf
dedicated, standardized device sanitize commands that apply ISM-specific techniques to bypass the abstraction inherent in typical read and write commands
Checked 2026-10-10.
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