Non-Volatile NAND Bitmap for PBA Garbage Collection
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Solution Overview
Problem
In NAND memory systems, the continuous overwriting of data leads to an increasing number of invalid physical block addresses (PBAs), resulting in inefficient use of memory and the need for frequent garbage collection, which can be resource-intensive and costly due to the reliance on volatile memory like RAM.
Innovation Solution
Implementing a bitmap in NAND memory cells to track the validity of data stored at each PBA, allowing for bit-level memory operations such as bit-level erase and program to maintain the bitmap, thereby reducing the need for volatile memory and enhancing data management efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If volatile memory (RAM) is used to track valid/invalid PBAs, then data management efficiency is improved, but cost and device complexity increase
Solution Approach 1:
The patent creates a copy of the PBA validity information directly within the non-volatile memory structure itself, eliminating the need for separate volatile memory. The bitmap is stored as part of the memory array, allowing the system to track valid/invalid PBAs without external RAM assistance.
Solution Approach 2:
The memory system uses its own non-volatile storage capacity to serve the management function that previously required separate volatile memory. The bitmap stored in non-volatile memory cells provides self-contained tracking capability, making the system self-sufficient without external memory dependencies.
2Reliability
If garbage collection is performed frequently to manage invalid PBAs, then data integrity is maintained, but productivity and energy efficiency deteriorate
Solution Approach 1:
The bitmap is updated in advance whenever data is written to or erased from a PBA, proactively tracking validity status before garbage collection is needed. This preliminary tracking eliminates the need for full memory scans during garbage collection operations.
Solution Approach 2:
The bitmap provides continuous feedback about the validity status of PBAs, enabling the garbage collection process to operate more efficiently by only processing actually invalid regions rather than scanning the entire memory space.
3Quantity of substance
If the number of invalid PBAs increases over time, then storage capacity utilization is improved, but the frequency and resource cost of garbage collection increases
Solution Approach 1:
The patent replaces the mechanical process of scanning and detecting invalid PBAs during garbage collection with an electronic bitmap lookup system. The bitmap stored in non-volatile memory provides direct digital indication of invalid regions, substituting complex detection mechanisms with simple read operations.
Data Source
AI summary
Technology for managing non-volatile memory. A bitmap may be maintained in NAND memory cells. The bits in the bitmap map to an address (e.g., PBA) in the NAND memory cells. Each bit has either a first value to indicate that the corresponding address stores valid data or a second value to indicate that the corresponding address does not store value data. Garbage collection may be performed based on the bitmap. Bit-level memory operations are performed to maintain the bitmap. Bit-level erase may be performed to erase a memory cell to have a value that indicates a valid/invalid status. The bitmap may contain unencoded data. In one aspect, a one's complement to the bitmap is stored in the NAND memory cells. The one's complement has opposite values as the regular bitmap. The system may compare the values in the regular bitmap and the one's complement bitmap for data integrity.