Flash Translation Layer Bad Block Remapping
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Solution Overview
Problem
Conventional flash memory devices cannot perform in-place updates on written data, leading to inefficient data management due to limited read and write operations and physical defects in memory blocks, necessitating the use of reserved or redundant blocks for bad blocks.
Innovation Solution
A method and apparatus for controlling memory device access by using a bad block bitmap to identify defective blocks and remap logical memory addresses to reserved physical addresses, employing a flash translation layer (FTL) with a bad block bitmap referencing unit and memory mapping unit to manage data operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a flash memory device performs read and write operations continuously, then data storage capacity is utilized, but memory blocks develop physical defects and become bad blocks
Solution Approach 1:
The system performs preliminary actions by detecting bad blocks proactively during normal operation and remapping them to reserved blocks before they cause data loss. The block mapping table is pre-configured with reserved blocks for each bad block, enabling preventive remapping rather than reactive error handling.
Solution Approach 2:
The system changes the parameter of block availability by dynamically updating the block mapping table to redirect access from failed blocks to reserved replacement blocks. This parameter change maintains system functionality despite physical degradation of memory cells.
2Reliability
If reserved blocks are allocated for each bad block, then bad block functionality is replaced, but memory device complexity increases
Solution Approach 1:
The memory device is segmented into functional blocks and reserved replacement blocks. The block mapping table is segmented to maintain separate mappings for normal blocks and bad block replacements, allowing independent management of each segment without affecting the entire system.
Solution Approach 2:
The block mapping table acts as an intermediary layer between the logical address space and physical memory blocks. It mediates access requests by translating logical addresses to appropriate physical blocks, hiding the complexity of bad block management from the host system.
3Reliability
If conventional bad block management is used without optimization, then bad blocks are detected, but write operation performance degrades
Solution Approach 1:
Bad blocks are detected and reserved replacement blocks are allocated in advance during manufacturing or initial operation. This preliminary detection and reservation eliminates the need for time-consuming detection and remapping operations during normal write operations, maintaining high write performance.
Solution Approach 2:
The flash memory device performs self-service by autonomously detecting bad blocks and managing remapping operations without host intervention. The controller automatically updates the block mapping table and redirects write operations to reserved blocks, eliminating performance overhead from host-side error handling.
Data Source
AI summary
An apparatus, memory device controller and method of controlling a memory device are provided. The example apparatus may include a bad block bitmap referencing unit configured to obtain bad block information from a bad block bitmap based on a given memory address, the given memory address being one of a logical memory address and a physical memory address corresponding to the logical memory address, the bad block information indicating whether a given memory block corresponding to the given memory address is a bad block and a memory mapping unit configured to obtain the physical memory address corresponding to the logical memory address, and configured to obtain a reserved physical memory address corresponding to the physical memory address if the bad block information indicates that the given memory block is a bad block. In an example, the apparatus may be embodied as a memory device controller including a flash translation layer (FTL).