Data security on SSDs is a mess. Good luck removing data! Preserve it for digital forensics? Uh-oh. Secure erase might work, but it that good enough?

SSD data recovery

SSD security is important because data recovery is so much easier than for hard drives. For less than $1k you can buy the equipment that will read flash chips.

Flash SSD architecture leaves sensitive data at risk. Unlike hard drives, when flash SSDs rewrite a block, they don’t overwrite a fixed block: they grab some empty block and write over that, leaving the original data untouched.

Architectural insecurity

Flash is written to the first free 128k or 256k blocks. Rewriting means making a copy of the block and writing the old data plus the new data to another block.

Flash drive controllers virtualize the flash capacity through the flash translation layer (FTL). The blocks your OS sees are not the blocks that are being written. In addition, flash SSDs maintain a large pool of capacity that is not seen by the operating system.

Which leaves your old data on the old block. New writes are written to the first free location, not, as on a disk, to a specified physical location.

Garbage collection eventually overwrites the old block to adds it to the free block pool. Cheaper MLC drives avoid aggressive garbage collection because it wears out the drive sooner.

In addition, the flash failure mode is that the block cannot be written. As blocks reach their end of life, they may not get rewritten at all – leaving sensitive data there for years.

In the meantime you can have 10’s of gigabytes of data sitting on capacity that your OS can’t see. And like hard disks, “deleting” a file does nothing of the sort.

via SSD security: the worst of all worlds | ZDNet.