Re: Page corruption when writing non-sequential pages in an MLC NAND eraseblock

[Romain Izard <romain.izard.pro@gmail.com>]

On 2013-10-01, Avery Pennarun <apenwarr@gmail.com> wrote:
> Hi everyone,
>
> Does this sound familiar?
>
> Setup:
> - Linux 2.6.37 or 3.2.26 (apologies for the old versions, but I
> couldn't find any related patches in newer kernels and these are
> embedded systems that are a bit hard to upgrade)
> - Micron MT29F16G08CBACAWP - MLC NAND
> - 1 Mbyte eraseblocks
> - 1 kbyte pages
> - Tested on two different hardware platforms (MIPS and ARM devices)
>
> Steps:
> - Disable ECC to avoid any confusion (ECC turns out to not affect the
> test results, but I wanted to make sure)
> - Erase any eraseblock
> - Write all-zeroes to page 0x18 of that eraseblock; read it back -> ok
> - Write all-zeroes to page 0x12 of that eraseblock; read it back ->
> FAIL, all 0xff instead
> - Read page 0x18 -> completely random data (about 12% of bits are flipped)
>
> More details:
> - It doesn't happen with a related Micron SLC NAND
> - If you write the pages in the opposite order there is no problem
> - Delays before/after reading and writing, and the sequence of reads,
> has no effect
> - This turns out to happen for any pair of pages, where pairs are
> always exactly 6 pages apart (n and n+6), other than the first and
> last 4 pages in each eraseblock, which are paired with different pages
> to make the math work out
>
> I've read about the concept of MLC "paired pages" causing corruption
> elsewhere, but it supposedly only happens when you get a power
> failure.  It's happening for me during normal runtime, which seems
> wrong.

For me you're violating one key MLC assumption: the pages within a block
must be written in a strictly increasing order. It should be written
somewhere in the component's datasheet.

Best regards,
-- 
Romain Izard