2Gbit and 4Gbit version of the Micron SPI NAND flash used on Bus Pirate 5. 

Bus Pirate 5 is mounted with a 1Gbit MT29F1G01ABAGDWB-IT:G NAND flash chip that formats to approximately 100 megabytes. The page size is 2K, it has a single plane of flash.

 MT29F2G01ABAFDWB has 2Gbit of NAND flash. The page size is also 2K, but it has two planes to select from. Upgrading to this flash chip would probably involve changing the end address/number of pages in the nand.h flash setup files and figuring out how to switch planes. Planes could be swapped on the fly, or used as two separate partitions. I have not looked that closely.

 MT29F4G01ABAFDWB is the 4Gbit NAND version. The page size is 4K, but it only has a single plane. Upgrading to this flash chip could involve expanding the read/write buffer in the nand.c/h functions and updating the end address. 

Swap chips at your own risk. There's no software or firmware support (planned) for these chips, but the Bus Pirate is a hacker tool and things happen.