Non-Volatile Journal for Incomplete Write Group Recovery
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Solution Overview
Problem
Open Channel SSDs lack recovery mechanisms for managing write groups, leading to potential data loss due to uncorrectable errors and incomplete writes, especially during power failures, as they do not support power fail protection and may acknowledge writes before data is flushed to non-volatile storage, resulting in write holes and difficulty in determining completed write groups.
Innovation Solution
A solid state drive system with a non-volatile journal and command handler that sends event notifications to the host for incomplete write groups, using a write group journal to identify and notify of data loss events, and includes a cache memory to store write data blocks and metadata for destination page addresses, ensuring data integrity and recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the storage device acknowledges writes after writing to volatile cache before flushing to non-volatile media, then write performance is improved, but data reliability deteriorates due to potential write holes during power failures
Solution Approach 1:
The patent implements a journaling mechanism that records write operations in a journal structure before they are committed to the cache. This preliminary action creates a recoverable record of writes that were acknowledged but not yet flushed to non-volatile storage, allowing the system to recover and identify incomplete writes after a power failure without changing the performance-optimized write path.
2Reliability
If the host implements consistency checks after power failure to determine completed write groups, then data consistency is improved, but device availability deteriorates due to prohibitively long check durations
Solution Approach 1:
The journal structure is prepared in advance with metadata that tracks the completion status of each write group. During normal operation, the journal is continuously updated with write acknowledgments and flush completions. After a power failure, the recovery process simply needs to scan this pre-prepared journal structure rather than performing expensive consistency checks across the entire storage device, dramatically reducing recovery time and maintaining high availability.
Solution Approach 2:
The journal structure acts as an intermediary between the write operations and the recovery process. It provides a simplified, pre-processed view of write group completion status that the host can quickly scan and interpret, eliminating the need for complex consistency checks while ensuring data consistency after power failures.
3Device complexity
If the storage device does not implement recovery mechanisms like RAID configurations, then device complexity is reduced, but data loss risk increases due to uncorrectable errors and incomplete writes
Solution Approach 1:
The patent segments the write tracking function into a separate journal structure that operates independently of the main storage operations. This segmentation allows the recovery mechanism to function as a lightweight add-on that tracks write group completion without requiring complex RAID configurations or integrated recovery hardware, maintaining low device complexity while providing robust protection against data loss from uncorrectable errors and incomplete writes.
Data Source
AI summary
Example storage systems, storage devices, and methods provide a write group journal for identifying incomplete writes. Related write request indicators are stored in a non-volatile journal in a solid state drive to identify a related write group and indicate whether the related write group has been stored in storage locations corresponding to physical page addresses. An event notification is sent to a host system when the related write request indicator indicates that the group was incomplete at the time of a data loss event.