On 10/30/2019 10:16, Dennis Lee Bieber wrote:

>  Since most flash memory erases to 1s, the first half is mostly a no-op.
> The card obtains an allocation unit from its free-list, erases it, and then
> essentially does nothing but declare the sectors in use as writing all 1s
> to a unit filled with 1s makes no changes.
>
>  1-bits can be changed to 0-bits but I doubt the SD card controller chip
> is smart enough to realize it can do an in-place update -- so again the
> card will obtain a free allocation unit, erase it to 1s (and copying any
> data belonging to other unopened files to the unit), then write 0s to the
> sectors of the opened file.

So would it make more sense to just write a file of 0s and then erase
it?  And to change the file size to 4MB?  Or does every write to a file
whether the same data or not cause an erase and a write to a different
block?  I which case we could just write 0s to the file over and over again.

--

Knute Johnson

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