"And some drives don't erase all that data," said Gregory Wong, an analyst with market research firm Forward Insights.
For example, on most of today's SSDs wear-leveling algorithms are used to more evenly distribute data across the drive so as to not wear out any one area of the NAND flash. The problem is, wear leveling can also defeat data erasure because it relocates blocks between the time when they are first written and then overwritten.
The National Institute of Standards and Technology (NIST) is currently being pushed by the SSD industry to redefine some of the military erase overwrite protocols to recognize encrypting drives that can be cryptographically erased without the need to overwrite the flash.
"But that's not happening tomorrow. Government agencies take a long time to embrace standards," Smith said.
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