Stefan Monnier writes:
> > To test, say with a 16 GB SD, fill the SD to all except the last 1 KB,
> > and with a looping script, write 1KB of 1's to the remainder of the
> > SD, erase the "bits," then 1KB of 0's, erase the "bits", and so on;
>
> I'm surprised. I would have expected uSD cards, just like SSDs to rely
> mostly on a (small) amount of extra storage, i.e. the actual amount of
> NAND storage is higher than that reported as being available.
>
> This way the uSD card knows for sure which blocks are in use and which
> ones aren't (without having to rely on things like TRIM).
>
That's true, Stefan, and most SD cards are made with a larger size of
physical memory than specified-inoperable bits can be mapped
out/replaced during product QA/test. The remaining bits can be used
for R/W, but, sooner or later, they wear out too-only delaying the
inevitable in the above test.
Quality SSDs will continue the mapping of inoperable bits through the
life cycle of the device-but requires some sort of ECC to do the real
time analysis, (archival grade SDs used to do this, but that market
has deteriorated because of the additional expense.)
John
--
John Conover, cono...@panix.com, http://www.johncon.com/
