FTL (Flash Translation Layer)

Flash’s Limitation

• No overwrite without Erase
• Big erase block : ex. 2MB
• Factory Bad Block and Run time Bad Block
• Run time bit error
• Limited Lifetime : ex) Erase 5K for an Erase Block

FTL’s Roles

• Flash Translation Layer : mapping virtual sector to physical block
• Garbage Collection
• Power Loss Recovery
• Error Correction
• Bad Block Management
• Wear leveling

Address Remapping

• Address mapping table
• Trying to update data of (Sector #3045) stored NAND(Block #125, Page #29)

Sector Mapping

LSN: Logical Sector Number PSN : Physical Sector Number

Block Mapping

LBN: Logical Block Number PBN : Physical Block Number

Hybrid Mapping

Merge

Garbage Collection

Spare Space method

• Mitsubishi
• Data space : in-place
• Spare space : out-of-place

Mirror Block method

• M-Systems (FMAX)

Log Block method

• SNU
• write (5,1) (5,1) (5,2) (5,4) (5,4) (5,1)
• write (6,3) (8,0) (8,1) (8,2) (8,3) (8,4) (8,5)

Full Associative Sector Translation : FAST

• write (5,1) (5, 1) (6. 2) (6, 4) (8, 4) (5, 1), (8, 3)