Magnetic Disk Controller Bit Inversion for Flash Write Time
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Solution Overview
Problem
Conventional magnetic disk apparatuses face challenges in efficiently saving user data during power loss due to the increased time required for writing data onto flash memory when the number of first values (high voltage side) in user data is high, and the limited backup power available.
Innovation Solution
The magnetic disk apparatus includes a controller that performs bit inversion of user data in the volatile memory and writes it onto the flash memory when the number of first values is higher, and writes without bit inversion when the number of first values is lower, thereby controlling the total number of first values stored in the flash memory to reduce saving time and prevent data loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is written onto flash memory during power loss, then data loss is prevented, but the time required for writing increases when the number of first values is high
Solution Approach 1:
The controller changes the parameter of bit inversion based on the number of first values in the data. When the number of first values exceeds a threshold, the controller inverts bits of the data before writing to flash memory. This parameter change transforms data with high first value counts into data with lower first value counts, reducing writing time while maintaining data integrity and preventing loss.
2Loss of time
If bit inversion is performed to reduce writing time, then saving time is improved, but the complexity of data processing increases
Solution Approach 1:
The controller implements a conditional parameter change based on counting the number of first values in the data. This simple counting and conditional inversion approach avoids complex data processing while achieving time reduction. The threshold-based decision logic keeps the processing complexity manageable.
Solution Approach 2:
The invention applies bit inversion as a straightforward transformation to flip bits in the data. This inversion operation is computationally simple and directly reduces the number of first values, thereby reducing writing time without introducing significant processing complexity.
3Reliability
If data is written to flash memory, then data loss is prevented, but memory cell transistor capacity degradation increases
Solution Approach 1:
The controller changes the data parameter through bit inversion when the number of first values is high, thereby reducing the total number of first values written to flash memory. This reduces the frequency of charge pumping operations on memory cell transistors, slowing down capacity degradation and extending their operational duration.
Solution Approach 2:
The invention converts the potentially harmful effect of high first value counts (which cause longer writing times and more wear) into a benefit by inverting bits. This transformation turns data with high first value counts into data with lower first value counts, reducing wear on memory cell transistors and extending their lifespan.
Data Source
AI summary
According to a magnetic disk apparatus of one embodiment, threshold voltages of memory cell transistors of a flash memory are set to a first section for a first value or to a second section for a second value. The second section is on a lower voltage side than the first section. The controller performs bit inversion of second data held in a volatile memory and writes the second data onto the flash memory when a power loss occurs while the second data corresponds to third data in which a number of the first values is larger than that of the second values. The controller writes the second data onto the flash memory without bit inversion when a power loss occurs while the second data corresponds to fourth data. The fourth data is data in which a number of the first values is smaller than that of the second values.