RAID Controller Proactive Rebuild for Read Tail Latency
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Solution Overview
Problem
Non-volatile storage systems, particularly SSDs with NAND flash memory, experience high read tail latencies due to asynchronous background management activities and architectural characteristics, which existing strategies fail to fully address or require significant system changes.
Innovation Solution
A RAID controller proactively rebuilds data upon detecting high latency read requests, determining the necessity based on monitoring and available redundancy, to reduce access latency without data errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If existing strategies (program/erase suspend, I/O command scheduling, background maintenance control) are implemented to reduce read tail latencies, then read access performance may be improved, but system complexity increases significantly
Solution Approach 1:
The patent performs RAID rebuild operations proactively during idle periods or low-utilization windows before high-latency issues affect read performance. By anticipating and executing rebuilds in advance, the system prevents latency degradation without requiring complex real-time intervention mechanisms
Solution Approach 2:
The system automatically monitors its own performance metrics and triggers rebuild operations based on detected latency patterns, eliminating the need for external complex control systems. The storage array self-regulates by identifying when rebuilds are beneficial and executing them autonomously
2Loss of time
If proactive RAID rebuild is initiated for every high latency read request, then read tail latencies are reduced, but system productivity decreases due to excessive rebuild operations
Solution Approach 1:
The patent applies partial action by selectively triggering rebuild operations only for specific high-latency read requests rather than all such requests. The system evaluates individual request characteristics and initiates rebuilds only when the expected performance benefit outweighs the cost, avoiding excessive rebuild operations that would degrade overall productivity
Solution Approach 2:
The system dynamically adjusts rebuild initiation parameters based on system state, including latency thresholds, current utilization, and rebuild history. By changing these parameters adaptively, the system optimizes the balance between reducing read latencies and maintaining overall system productivity
3Loss of time
If RAID rebuild is performed to reduce read tail latencies, then data access performance improves, but the risk of data loss increases if not managed properly
Solution Approach 1:
The patent prepares cushioning measures by verifying data integrity and ensuring proper RAID configuration before initiating rebuild operations. This beforehand preparation ensures that rebuilds are performed safely and that data integrity is maintained throughout the process, preventing potential data loss
Data Source
AI summary
A data storage system includes a plurality of storage devices organized as a redundant array of inexpensive disks (RAID) storage array and a RAID controller. The RAID controller monitors the plurality of storage devices in the RAID storage array. The RAID controller also detects that a host read request of a host has a latency exceeding a latency threshold. Based on the monitoring, the RAID controller determines whether a proactive rebuild of a data requested by the host read request in absence of a data error would likely be beneficial to performance. Based on determining that a proactive rebuild of the data requested by the host read request would likely be beneficial to performance, the RAID controller initiates the proactive rebuild of the data and sends the requested data to the host.