Hybrid Drive Command Queue Balancing for NVSM and Disk
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Solution Overview
Problem
Hybrid disk drives face challenges in balancing the execution times of disk and non-volatile semiconductor memory (NVSM) command queues due to mechanical latency and write amplification, leading to inefficiencies and potential errors that affect performance.
Innovation Solution
Implementing a control circuitry that estimates and balances the execution times of disk and NVSM command queues by transferring access commands between them based on estimated and actual execution times, using algorithms to reorder commands and apply migration policies to optimize data storage and retrieval.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If data is stored frequently accessed in NVSM to reduce access time, then access speed is improved, but write amplification increases reducing NVSM longevity
Solution Approach 1:
The patent implements dynamic command queue balancing that continuously monitors and adjusts the distribution of commands between disk and NVSM based on current execution times. This dynamic approach allows the system to adapt to changing workloads and data access patterns, optimizing the trade-off between access speed and NVSM wear by flexibly routing commands to the most appropriate storage medium at any given moment
2Loss of time
If commands are preferentially executed from NVSM to maximize speed, then access time is reduced, but execution time imbalance between disk and NVSM increases
Solution Approach 1:
The patent employs feedback mechanisms where the controller monitors actual command execution times from both disk and NVSM, compares them against target execution times, and uses this information to dynamically adjust command queue balancing. This closed-loop control ensures that the system maintains balanced execution times while maximizing overall access speed, preventing either storage medium from becoming a bottleneck
3Productivity
If command queue balancing is implemented to balance execution times, then system efficiency is improved, but control complexity increases
Solution Approach 1:
The patent implements a self-service command queue balancing system where the controller automatically monitors execution times, determines imbalances, and redistributes commands between disk and NVSM without external intervention. The system uses predetermined target execution times and automatic adjustment algorithms to maintain balance, reducing the need for complex manual control while improving system efficiency through autonomous optimization
Data Source
AI summary
A hybrid drive is disclosed comprising a head actuated over a disk, and a non-volatile semiconductor memory (NVSM). A first execution time needed to execute commands in a NVSM command queue is estimated, and a second execution time needed to execute commands in a disk command queue is estimated. An access command is inserted into a selected one of the NVSM command queue and the disk command queue in response to the first and second execution times, and one of the first and second execution times is updated in response to an estimated execution time of the access command.