NAND flash memory, as well as other types of non-volatile memories (“NVMs”), are commonly used in electronic devices for mass storage. For example, consumer electronics such as portable media players often include flash memory to store music, videos, and other media.
Non-volatile memories, however, may develop defective memory cells through everyday use, and operational memory cells may suffer from program/erase/read disturb due to voltages applied to neighboring cells. When a memory location, such as a page, of a NVM contains too many defective cells or otherwise becomes unusable from excessive errors, the information contained within that memory location may be lost. When this occurs, the electronic device using the NVM might lose user data (e.g., data stored by an application) or data that keeps track of the location of pages in the NVM (e.g., pages that store a logical-to-physical mapping). If a page that stores the logical-to-physical mapping experiences an uncorrectable error (e.g., it is lost), the NMV system may not be able to use the data contained therein to translate between a logical address and a physical address. Such pages are referred to herein as index pages.
In some operations such as garbage collection, the occurrence of an uncorrectable error (e.g., an unreadable memory location) in an index page can have substantial adverse effect on the management of the NVM.