A question posted on Quora — “In NAND memory, why is there a limit to the times we can make a partial write to a page? Is it because of write disturb. If so how does it happen? Does the same apply to partial reads?”
Having worked for some time on SLC NANDs, few points which comes to my mind are :
NAND data sheets from Samsung, Toshiba & Micron tend to limit the number of times a page can be partially programmed (usually to 4), this may be a circuit design decision which might have aided in some optimization with cost/speed/reliability etc. The exact reason could be only given by the NAND chipset designers.
Did observe that if we try, then we could partially program pages for more than the actually mentioned 4 times. But reliability is a question here! Four cycles of partial programming is a good number, if your software is doing frequent partial writes then it is inviting a performance hit.
Read disturbances are known to cause bit flips and excessive number of block erase cycles can lead to bad blocks. Not aware of any “write disturb”on SLCs.
NAND page read protocol will always fetch the data from the cells into an internal NAND chip RAM buffer from there the data can be sampled though any multi pin interface. In that sense, have not come across any hardware which allows partial read of physical NAND pages. We can definitely do random partial reads on a page after it is fetched from the NAND cells into this internal NAND chip buffer, but then this can be executed unlimited number of times