Pcfree has just Released A Real 1:1 Wii NAND Dumper Enjoy.
This program is a 1:1 Wii NAND Dumper based on YaWnD 0.3 with several improvements. All currently available Wii NAND Dumpers misunderstand the IOS_Read() returned error code -12 and cause dumped image file to be different from extracted image of external hardware programmer for de-soldered NAND chip.
After analyzing, the -12 code seems very likely to be ECC error but not simply to be bad block. And most pages with -12 return code might be unmanaged free block (ECC error due to erased but not programmed yet). Zeroing these pages is a bit dangerous. If it happens it's the very first time the ECC error occurred for a good page while dumping, zeros it might cause the dumped image useless.
Besides the -12 code, some people encounters -11 code and stop their dumping. I guess the -11 code might be NAND read timeout and NAND status error. Stopping dumping is not a good idea but zeroing it would be safe. I also provide extra Page Debug Dump for these -11 code for user to analyze it.
For whose NAND dump without -11 code, the RealWnD can help them make 100% 1:1 dump which is exact the same with hardware programmer dump.