SSD Read-Only Mode After PLP Backup Failure
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Solution Overview
Problem
Traditional SSDs face challenges in ensuring data integrity during power loss events due to the failure of power loss protection (PLP) components, leading to potential data loss and unrecoverability, especially as SSDs age, and existing solutions like continuous metadata logging are inefficient and unsuitable for large-scale operations.
Innovation Solution
The method involves identifying critical metadata and storing it in non-volatile memory, creating a first table of contents, and upon power restoration, determining which table of contents to point to in order to enter either read-only or read-write mode, thereby reducing the risk of data loss and maintaining SSD functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all volatile data including non-critical metadata and cache data is hardened during power loss event, then data integrity is improved, but hardening time and energy consumption increase
Solution Approach 1:
The patent segments volatile data into critical metadata and non-critical data (cache and non-critical metadata). Only critical metadata is hardened during power loss events, while non-critical data is discarded. This segmentation allows the system to maintain data integrity for essential operations without the time penalty of hardening all data.
Solution Approach 2:
The patent extracts and identifies only the critical metadata portion of volatile data for hardening operations. By separating critical from non-critical data, the system performs hardening only on the essential subset, reducing hardening time while preserving data integrity for operations that require it.
2Stability of the object's composition
If table of contents is written only after all data is saved, then data consistency is improved, but risk of complete unrecoverability increases when PLP fails
Solution Approach 1:
The patent performs preliminary hardening of critical metadata before attempting to harden all data and write the table of contents. This preliminary action ensures that even if PLP fails during the complete hardening process, the critical metadata is already preserved in non-volatile memory, maintaining system recoverability.
Solution Approach 2:
The patent implements a cushioning mechanism by first hardening critical metadata to non-volatile memory before proceeding with full data hardening. This creates a safety buffer that prevents complete system unrecoverability if power is lost during the subsequent hardening operations or table of contents writing.
3Reliability
If metadata logs are created continuously at runtime, then data recovery capability is improved, but SSD latency increases due to competing write operations
Solution Approach 1:
The patent extracts only the essential critical metadata that needs to be preserved, rather than continuously logging all metadata operations. This selective approach maintains data recovery capability for essential operations without the performance overhead of continuous comprehensive logging.
Solution Approach 2:
Instead of implementing complete continuous logging of all metadata operations, the patent applies partial action by only tracking and hardening critical metadata. This reduces the logging overhead and associated latency while still providing sufficient data recovery capability for essential operations.
4Reliability
If PLP components are designed to harden all volatile data, then data protection is improved, but energy requirements exceed available backup power especially as SSD ages
Solution Approach 1:
The patent segments volatile data into critical and non-critical portions, allocating PLP energy resources only to harden critical metadata. This segmentation enables the system to provide adequate data protection for essential operations within the energy constraints of aging PLP components.
Solution Approach 2:
The patent implements partial hardening action by focusing PLP energy resources exclusively on critical metadata rather than attempting to harden all volatile data. This partial approach ensures data protection for essential operations while keeping energy requirements within the available backup power capacity.
Data Source
AI summary
A method of operating a Solid State Drive (SSD), comprising identifying critical metadata corresponding to data previously written to the SSD. In response to a power loss event the method also includes storing the critical metadata in a non-volatile memory. Further, the method also involves writing a first table of contents corresponding to the stored critical metadata to the non-volatile memory and storing a pointer to the first table of contents. A Solid State Drive (SSD) including a memory controller, a non-volatile memory, and a power loss protection capacitor. The memory controller is configured to identify critical metadata corresponding to data previously written to the SSD. The memory controller is also configured to, in response to a power loss event, store the critical metadata in a non-volatile memory write a first table of contents corresponding to the stored critical metadata to the non-volatile memory, and store a pointer to the first table of contents.