Tiered Storage Controller Extent Group Correlation
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Solution Overview
Problem
Tiered storage systems face inefficiencies due to high overhead and time consumption in data transfer between tiers based on periodic access frequency evaluations, which affects performance and cost optimization.
Innovation Solution
A storage controller that determines correlated logical extents and transfers them collectively as extent groups between high-speed and low-speed storage devices, using tables like the extent management table and extent group management table to manage access and data relocation, thereby reducing data transfer overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If periodical access frequency evaluation is used to transfer data between tiers, then data placement accuracy is improved, but data transfer overhead increases and processing time is consumed
Solution Approach 1:
The patent applies preliminary action by evaluating access frequency and determining data placement decisions continuously in the background before actual data transfer is needed. The storage controller pre-identifies extents that should be moved between tiers based on accumulated access statistics, so that when transfer is initiated, the decision-making process has already been completed, reducing the time penalty of periodic evaluation.
Solution Approach 2:
The system implements self-service by having the storage controller automatically monitor its own access patterns and make autonomous decisions about data placement without external intervention. The controller evaluates access frequency for each extent and autonomously determines when and where to transfer data, eliminating the need for manual management or complex external scheduling mechanisms.
2Measurement precision
If periodical access frequency evaluation is used to transfer data between tiers, then data placement accuracy is improved, but data transfer overhead increases
Solution Approach 1:
By performing access frequency evaluation and transfer decision-making in advance, the system prepares data placement decisions before actual data movement occurs. This preliminary evaluation allows the system to batch and optimize transfer operations, reducing the overhead associated with frequent, reactive data movements between tiers.
Solution Approach 2:
The patent changes the parameter of evaluation frequency from periodic to continuous or near-continuous monitoring. By tracking access frequency continuously rather than at fixed intervals, the system maintains accurate placement decisions while reducing the total number of transfer operations needed, thereby lowering the energy overhead associated with data movement.
3Productivity
If data is transferred between tiers based on access frequency, then storage system performance is improved, but operational costs increase
Solution Approach 1:
The patent applies local quality by differentiating data placement strategies based on local access patterns of individual extents rather than applying a uniform policy across all data. The storage controller evaluates access frequency for each extent separately and places data locally in the most appropriate tier based on its specific access characteristics, optimizing performance for each data piece while minimizing overall operational costs.
Solution Approach 2:
The system changes the operational parameter from periodic batch evaluation to continuous monitoring with threshold-based triggering. By continuously tracking access frequency and triggering transfers only when thresholds are exceeded, the system maintains high performance responsiveness while reducing the total volume of data transfers, thereby lowering operational costs associated with data movement between tiers.
Data Source
AI summary
According to one embodiment, a tiered storage system includes a first storage device, a second storage device and a storage controller. The storage controller determines, when a range of an access request to a logical unit extends over some of logical extents in the logical unit, that these logical extents are correlated with each other. The storage controller transfers data of a set of the correlated logical extents as one extent group collectively in units of physical extents between the first storage device and the second storage device.