Hybrid Drive Write Reordering via Nonvolatile Cache Segmentation
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Solution Overview
Problem
Existing hard disk drives (HDDs) face limitations in random write performance due to the inefficiency of write command reordering, particularly when dealing with long command queues, which restricts the rate at which data can be transferred to a non-volatile medium.
Innovation Solution
Implementing a hybrid drive system that uses a nonvolatile solid state memory device as a cache for a magnetic storage disk, allowing data to be written directly to the solid state memory without intermediate storage in a DRAM buffer, and strategically selecting and reordering data blocks based on factors like recency and proximity to the read/write head for efficient transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If write commands are reordered to improve random write performance, then write throughput increases, but the time required to reorder the command queue increases, limiting the effectiveness of long command queues
Solution Approach 1:
The patent divides the command queue into multiple segments or zones based on seek time characteristics. By segmenting the queue, the system can perform reordering operations on smaller subsets of commands rather than the entire queue, reducing the time required for reordering while still achieving improved random write performance through optimized command sequencing within each segment.
2Productivity
If data is written directly to nonvolatile solid state memory without using DRAM buffer, then data transfer rate increases, but the complexity of data management and caching strategies increases
Solution Approach 1:
The patent introduces a nonvolatile solid state memory device as an intermediary between the host system and the magnetic storage disk. This intermediary serves as a cache that absorbs the complexity of data management, allowing direct writing from host to solid state memory while the system handles caching, buffering, and data movement strategies to manage the complexity internally.
3Productivity
If the command queue size is increased to allow more write commands to be reordered, then write performance improves, but the reordering time exceeds the write command execution time, making it impracticable
Solution Approach 1:
The patent performs preliminary reordering actions on incoming write commands as they are added to the command queue, rather than waiting to reorder the entire queue before execution. By performing reordering operations incrementally and preliminarily as commands arrive, the system maintains a continuously optimized queue without requiring lengthy batch reordering operations that would exceed write execution time.
Data Source
AI summary
A hybrid drive and associated methods increase the rate at which data are transferred to a nonvolatile storage medium in the hybrid drive. By using a large nonvolatile solid state memory device as cache memory for a magnetic disk drive, a very large number of write commands can be cached and subsequently reordered and executed in an efficient manner. In addition, strategic selection and reordering of only a portion of the write commands stored in the nonvolatile solid state memory device increases efficiency of the reordering process.