Solid-State Storage FUA Write Latency Reduction
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Solution Overview
Problem
Existing solid-state mass storage devices face performance degradation and complexity in processing Forced Unit Access (FUA) write commands due to the need for double flash page writes and tracking metadata updates, which can lead to data loss during power failures.
Innovation Solution
A solid-state mass storage device with an auxiliary power supply that writes data and metadata separately, allowing immediate completion status return to the host system, and uses the auxiliary power to ensure metadata is flushed to non-volatile memory during a power failure, reducing the need for tracking updates and minimizing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the memory controller waits for metadata to be flushed to non-volatile memory before returning completion status for FUA write commands, then data integrity is ensured, but write performance degrades due to increased latency
Solution Approach 1:
The patent segments the FUA write command completion into two independent phases: (1) data write completion to non-volatile memory, and (2) metadata flush completion to non-volatile memory. The memory controller returns completion status to the host after phase (1) is complete, without waiting for phase (2). This segmentation allows the system to ensure data integrity while reducing write latency, as the metadata flush can complete asynchronously in the background.
2Reliability
If the memory controller tracks metadata updates to ensure proper flushing during power failures, then data integrity is maintained, but device complexity increases
Solution Approach 1:
The patent implements preliminary action by having the memory controller immediately write metadata to the L2P log in volatile memory upon receiving a FUA write command, before the data write completes. This preliminary metadata writing ensures that if a power failure occurs during the data write process, the metadata is already prepared and can be quickly flushed to non-volatile memory, eliminating the need for complex tracking mechanisms to monitor metadata update status.
3Reliability
If the memory controller flushes the entire L2P table copy to non-volatile memory during operation, then data integrity is improved, but productivity decreases due to performance impact
Solution Approach 1:
The patent extracts only the necessary metadata entries that correspond to uncommitted FUA write commands and flushes only those specific entries to non-volatile memory during power failure scenarios, rather than flushing the entire L2P table copy during normal operation. This selective extraction approach maintains data integrity for critical operations while avoiding the performance penalty of full table flushes during regular write operations.
Data Source
AI summary
Mass storage devices and methods of operating thereof adapted for use with a host and for storing data thereof includes at least one non-volatile memory for storing the data, at least one volatile memory, a memory controller configured for reading and writing the data and metadata to and from the non-volatile memory and the volatile memory, and an auxiliary power supply, wherein the memory controller locates the data on the non-volatile memory with the metadata. When processing a write command that requires all data to be written to the non-volatile memory before confirmation is returned to the host computer system that the write command has succeeded, the mass storage device is configured to write the data to the non-volatile memory, write the metadata to the volatile memory, and once the both data and metadata are written, return a completion status of the write command to the host computer system.