Flash Memory Power-Off Sequence Detection via Standby Logging
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Solution Overview
Problem
Existing data backup technologies for NAND-type flash memory systems, such as SSDs, cannot reliably maintain data consistency and protect management information during unexpected power-offs, as they lack efficient methods to differentiate between normal and abnormal power-off sequences.
Innovation Solution
A memory system comprising a volatile and nonvolatile storage unit, with a read/write control unit, log control unit, log reflecting unit, operating state managing unit, and management-information restoring unit, which uses a management table and logs to ensure data integrity and detect power-off sequences, storing difference logs and reflecting them in the nonvolatile storage upon specific conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multi-value memory technology is employed to increase storage capacity, then storage density is improved, but data consistency and reliability during power-off events deteriorates
Solution Approach 1:
The patent applies preliminary action by storing a standby log indicating normal power-off sequence before actually powering off. This log is written in advance to the nonvolatile storage unit, so that when power is restored after an unexpected power-off, the system can check whether the standby log exists to determine if a normal power-off sequence occurred. This preemptive logging mechanism ensures data consistency is maintained even though multi-value memory technology increases storage capacity.
2Reliability
If snapshot and log backup technology is used for hard disk devices, then data recovery capability is improved, but the technology cannot be applied to NAND-type flash memory systems
Solution Approach 1:
The patent applies parameter changes by modifying the power-off detection mechanism to work with NAND-type flash memory characteristics. Instead of relying on continuous logging during power-off (which doesn't work for flash memory), the system changes the approach to using a standby log that is prepared in advance and checked after power restoration. This parameter change in the detection methodology enables snapshot and log backup technology to be successfully applied to NAND-type flash memory systems, improving both data recovery capability and adaptability.
3Reliability
If difference logs are stored in nonvolatile storage before being reflected in the management table, then data integrity is improved, but system complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the logging process into distinct components: a log control unit that manages log storage, a log reflecting unit that applies logs to the management table, and an operating state managing unit that tracks power-off sequences. This segmentation of functions allows difference logs to be stored in nonvolatile storage with improved data integrity, while the modular structure manages system complexity by assigning specific responsibilities to each unit.
Data Source
AI summary
A first log indicating that a system is running is recorded in a second storage unit before a first difference log is recorded in the second storage unit after system startup, and a second log indicating that the system halts is recorded in the second storage unit following the difference log, at the time of normal system halt, and it is judged whether normal system halt has been performed or an incorrect power-off sequence has been performed last time, based on a recorded state of the first and second logs in the second storage unit, at the time of system startup, thereby detecting an incorrect power-off easily and reliably.