On Mar 14, 2011, at 3:18 PM, Arnd Bergmann wrote: > On Monday 14 March 2011 19:50:27 John Watlington wrote: >> Cards that are in the state you describe are most likely dead due to >> running out of spare blocks. There is nothing that can be done to >> rehabilitate them, even using the manufacturer's secret code. >> In a disturbing trend, most of the cards I've returned for failure analysis >> in the past year have been worn out (and not just trashed meta-data >> due to a firmware error). > > Part of the explanation for this could be the fact that erase block > sizes have rapidly increased. AFAIK, the original XO builtin flash > had 128KB erase blocks, which is also a common size for 1GB SD and > CF cards.
> Cards made in 2010 or later typically have erase blocks of 2 MB, and > combine two of them into an allocation unit of 4 MB. This means that > in the worst case (random access over the whole medium), the write > amplification has increased by a factor of 32. > > Another effect is that the page size has increased by a factor of 8, > from 2 or 4 KB to 16 or 32 KB. Writing data that as smaller than > a page is more likely to get you into the worst case mentioned > above. This is part of why FAT32 with 32 KB clusters still works > reasonably well, but ext3 with 4 KB blocks has regressed so much. The explanation is simple: manufacturers moved to two-bit/cell (MLC) NAND Flash over a year ago, and six months ago moved to three-bit/cell (TLC) NAND Flash. Reliability went down, then went through the floor (I cannot recommend TLC for anything but write-once devices). You might have noticed this as an increase in the size of the erase block, as it doubled or more with the change. Cheers, wad _______________________________________________ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
