The format of the Nintendo 3DS's flash filesystem is currently undocumented. Reading of the flash chip is possible through pinouts on the motherboard and has been performed successfully but the data is encrypted and can't be understood without first decrypting it.
Each NAND partition is formatted by a FAT file system.
The NAND file system appears to be encrypted using AES.
|nand||CTR-NAND File System. (3DS)|
|twln||TWL-NAND File System. (DSi)|