Magnetic Disk Auxiliary-Data Writing Under Latency Limits
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Solution Overview
Problem
Magnetic disk devices experience performance degradation and data write delays due to the sudden need to stop writing auxiliary data when the latency limit is reached, leading to incomplete error correction or logging, which degrades subsequent data write performance.
Innovation Solution
A controller in the magnetic disk device estimates the time required for data write processes and selectively executes either a first write control for user data or a second write control for auxiliary data based on a specified latency limit, ensuring that auxiliary data is written at appropriate times to avoid performance degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the magnetic disk device executes data write process within the latency limit time, then the data write speed is improved, but the auxiliary data (ECC or log data) cannot be completely written, causing performance degradation of subsequent data write
Solution Approach 1:
The controller predicts whether auxiliary data can be completely written before actually writing user data. By performing this prediction action in advance and selecting appropriate write modes based on the prediction result, the system avoids the performance degradation that would occur if auxiliary data writing were interrupted later during latency limit enforcement.
2Loss of time
If the magnetic disk device stops writing auxiliary data when the latency limit ends, then the latency limit is satisfied, but the sudden execution of forced write procedure degrades performance
Solution Approach 1:
The controller performs a prediction of auxiliary data write completion before the latency limit expires. Based on this advance prediction, it selects a write mode that ensures auxiliary data is completely written before the latency limit ends, thereby avoiding the need for sudden forced write procedures and maintaining high data write performance while still complying with the latency limit.
3Reliability
If the magnetic disk device writes both user data and auxiliary data to each sector, then the data reliability is improved, but the data write time exceeds the latency limit
Solution Approach 1:
The controller dynamically selects between different write modes (first write mode writing both user and auxiliary data, second write mode writing only user data) based on predicted write completion timing. This dynamic adaptation allows the system to maintain high data reliability when time permits, while meeting latency limits when necessary, thereby balancing reliability and time requirements.
Solution Approach 2:
The controller changes the write mode parameter based on the predicted ability to complete auxiliary data writing within the latency limit. When prediction indicates sufficient time, the system uses the first write mode with both user and auxiliary data; when time is insufficient, it switches to the second write mode with only user data, thus adapting to time constraints while maintaining reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach prevents performance degradation and data write delays by ensuring that auxiliary data is written at optimal times, improving data reliability and adherence to latency limits without interrupting the data write process.
Implementation Method 1
a magnetic head provided to seek in the radial direction of the magnetic disk and which writes and reads data to and from the magnetic disk
Data Source
AI summary
According to one embodiment, a magnetic disk device includes a first write control section of writing first data and second data to each of the sectors of a predetermined track among the tracks, a second write control section of writing the first data to each of the sectors of a predetermined track among the tracks, and a selection control section of, when receiving a write command, estimating the time required from start of a process of the first write control section to end of the process, and selectively executing the process of the first write control section or a process of the second write control section by comparing the estimated time with a time limit specified in advance.