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If writing to an ssd wears out its cells but reading does not, does an ssd read cells to avoid unnecessary writes?

For example, suppose I already zero'd an SSD, would the SSD write anything at all if I were to try and re-zero it?

I think this may be covered by the general technique of SSD "data buffering & caching", but I've not read explicit details...

Is this dependent on the exact scenario, for example:
- The amount being written vs. the size of the SSD cache?
- The speed of the write being pushed vs. the speed SSD's reads (to check) and writes (as necessary)?
- The SSD controller?
- The SSD brand?

dumb0
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1 Answers1

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It might, or it might not. Without knowing the exact model and it's exact firmware I don't think you can tell (and even then, unless you wrote the firmware it's still hard to be sure).

It's safe to assume that an SSD (or basically any flash media) might not overwrite what you want it to, it could:

  • write any sector anywhere
  • move old sectors to normally inaccessible "reserve" areas
  • some use compression, so writing GB's of zeros could take up virtually no space & actually write almost nothing
  • some always use encryption (whether or not you enter a password), and issuing a special "wipe drive" command only forgets the old encryption key & sets a new one, writing virtually nothing. (I've read some could implement this very poorly too)

The only constant should be that if you just wrote zeros somewhere, then you should read back zeros from there. But what actually happens behind the scenes is almost a literal "black box".

Xen2050
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