Magnetic Disk Command Processing Latency Limit Table
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Solution Overview
Problem
Magnetic disk devices face inefficiencies in command processing due to mechanical latency and reordering challenges, leading to increased rotational latency and suboptimal command response performance, especially when handling a large number of commands with varying read and write ratios.
Innovation Solution
A magnetic disk device and command processing method that utilize a latency limit time determination table to dynamically adjust the execution order of commands based on the number of commands and read/write ratios, allowing for real-time response time control by selecting commands considering both aging time and latency limit times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If reordering process is performed to reduce mechanical latency, then access speed is improved, but command response performance deteriorates due to delayed command execution
Solution Approach 1:
The patent implements dynamic command selection by determining latency limit times based on the current number of commands in the queue and the read/write command ratio. This allows the system to adaptively adjust command execution priorities rather than using a fixed reordering strategy, resolving the contradiction between optimizing access speed and maintaining command response performance
Solution Approach 2:
The system changes the parameter of latency limit time based on queue depth and command type distribution. By adjusting this parameter dynamically, the system can prioritize commands appropriately to both reduce mechanical latency and maintain good command response performance
2Loss of time
If commands are executed in received order, then command response performance is maintained, but mechanical latency increases due to suboptimal disk head positioning
Solution Approach 1:
The patent introduces dynamic latency limit times that change based on the number of commands in the queue and the ratio of read to write commands. This dynamic approach allows the system to balance between maintaining command response performance and optimizing access speed through selective reordering
3Productivity
If reordering is performed without considering command aging, then access efficiency is improved, but commands may be delayed beyond acceptable response times
Solution Approach 1:
The system uses feedback from the command queue state (number of commands, read/write ratio) to dynamically adjust latency limit times. This feedback mechanism ensures that reordering decisions consider both processing efficiency and response time requirements, preventing commands from being delayed too long
Data Source
AI summary
According to one embodiment, a magnetic disk device includes a disk, a head, a command queue, a command residence time calculation unit calculating a residence time of each of commands in the command queue, a command information calculation unit calculating the number of the commands and a ratio, a limit time determination unit obtaining a latency limit time corresponding to the number of commands and the ratio, from a latency limit time determination table, and a command selection processing unit selecting a command to be executed, by considering the latency limit time.