SSD Save Operation Using First-Bit Backup Cells
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Solution Overview
Problem
Existing memory systems face challenges in ensuring data integrity and reliability during power failures, particularly in solid state drives (SSDs) with nonvolatile semiconductor memories like NAND flash, where incomplete write operations can lead to data loss.
Innovation Solution
The implementation of a memory system with a nonvolatile memory and a memory controller that performs a save operation by writing data to a separate memory cell when a first bit is stored but a second bit is not, and transmitting a completion response after the first bit is written, utilizing a write buffer and parity buffer to manage data integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a save operation is performed to ensure data integrity during power failures, then data reliability is improved, but write operation time and system complexity increase
Solution Approach 1:
The patent identifies and saves only the first bit of data that requires writing during a save operation, rather than waiting to save complete multi-bit data units. This preliminary action on the critical first bit ensures data integrity can be achieved faster, reducing the time penalty of save operations while maintaining reliability.
Solution Approach 2:
The patent segments the data writing process into individual bit operations, specifically targeting the first bit for save operations. This segmentation allows the save operation to complete faster by not waiting for all bits to be written, thus reducing write operation time while still providing data integrity protection.
2Reliability
If a save operation is performed to ensure data integrity during power failures, then data reliability is improved, but device complexity increases
Solution Approach 1:
The memory controller performs a preliminary check to identify which data units require saving, and then executes save operations only for the first bit of those data units. This preliminary identification and selective saving simplifies the control logic compared to saving entire data units or implementing complex rollback mechanisms, thus improving reliability without proportionally increasing device complexity.
3Speed
If only the first bit is written and completion response is transmitted immediately, then response speed is improved, but data completeness may be compromised
Solution Approach 1:
The patent transmits a completion response after writing only the first bit of each data unit, which is a preliminary action that provides fast response speed. The remaining bits are written subsequently without waiting for acknowledgment, balancing response speed with eventual data completeness through buffered writing.
Solution Approach 2:
The writing of remaining bits continues in the background after the completion response is transmitted, maintaining continuous useful action. This ensures data completeness is eventually achieved without blocking the response path, thus preserving both response speed and data completeness.
Data Source
AI summary
According to an embodiment, a memory system includes a nonvolatile memory and a memory controller. The nonvolatile memory includes a first memory cell configured to nonvolatilely store data of a plurality of bits including a first bit and a second bit, and a second memory cell configured to nonvolatilely store data of at least one bit. The memory controller is configured to execute a save operation in accordance with reception of a command from a host, in the save operation, write first bit data to the second memory cell in a case where the first memory cell stores the first bit data as the first bit and does not store data as the second bit, and transmit, to the host, a completion response to the command after the first bit data has been written to the second memory cell.