FTL Functions

Wear Leveling

• Wear leveling software monitors Flash erase block cycling and guarantees that all erase block are cycled about the same number of times.
• Some files are seldom changed, while others may be changed frequently. If all files were updated at the same frequency, wear leveling would not be necessary.

Handling Device Error

• Handing Bad Block for NAND
• NAND permits 1-2% factory or run time bad blocks
• BD tract this information through marking to the head of block or separate table

• BD have to have strategy to decide run-time bad block when read/write/erase error happens

• Handling Bit error for NAND
• One or a few bit error happens rarely in NAND.
• Error collection code can allow the area to live instead of throw it away by marking Bad block

Power Loss Problem

• Power loss break BD’s integrity in various way
• Crash BD and make BD be disable to mount

• Point wrong physical block for a virtual sector

• Lost Data Case