RAID Super Block Reconstruction for Dual Disk Failure
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Solution Overview
Problem
Conventional RAID systems cannot reconstruct data when two hard disks fail, leading to a system crash, as they are unable to recover into a degraded mode in such scenarios.
Innovation Solution
A method is implemented in a RAID system with at least three hard disks and a RAID controller, where data is read from super blocks across all disks, common data is written back to these blocks, and the configuration is restored to a degraded mode, allowing for the detection and duplication of intact data from failed disks to an external storage device, along with recording the location of defective blocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional RAID systems are used with standard fault tolerance mechanisms, then the system can handle single disk failures, but the system crashes when two disks fail simultaneously
Solution Approach 1:
The patent performs preliminary actions by creating deep copies of data blocks and parity information to external storage devices before failures occur. When two disks fail simultaneously, these pre-prepared copies enable immediate reconstruction without system crash, resolving the contradiction between standard fault tolerance and multiple failure scenario handling
Solution Approach 2:
The patent introduces an intermediary external storage device that acts as a buffer between the RAID array and failure scenarios. This external storage holds backup data blocks and parity information, serving as a mediator that enables reconstruction when standard internal redundancy is insufficient, thus improving reliability for multiple failure cases
2Reliability
If data is stored using standard RAID-5 parity distribution, then single disk failure can be recovered, but reconstruction becomes impossible when two disks fail
Solution Approach 1:
The patent segments the reconstruction process into distinct phases: identifying failed disks, retrieving data blocks and parity information from external storage, and systematically reconstructing data. This segmentation of the complex reconstruction process into manageable steps reduces overall complexity and enables handling of dual-disk failure scenarios
Solution Approach 2:
The patent creates deep copies of critical data blocks and parity information to external storage devices. These copies serve as reconstruction sources when two disks fail, simplifying the recovery process by providing ready-to-use backup data rather than requiring complex calculations from remaining disks
3Ease of operation
If the RAID system operates in degraded mode after single disk failure, then the system remains operational, but a second failure causes complete system crash
Solution Approach 1:
The patent implements beforehand cushioning by pre-storing backup data blocks and parity information in external storage devices. This prior preparation creates a cushion of redundancy that protects the system when transitioning from degraded mode (single failure) to critical state (second failure), preventing system crash and enabling continued operation
Solution Approach 2:
The patent makes the external storage device universal by using it for multiple purposes: storing backup data blocks, storing parity information, and serving as a reconstruction source for various failure scenarios. This multi-functionality enables the system to handle both single and dual disk failures, improving reliability while maintaining ease of operation
Data Source
AI summary
The present invention is to provide a method for reconstructing data in case of failure of two HDs of a RAID, wherein the RAID is a logical disk drive assembly including at least three HDs and a RAID controller and data is divided into block strips which are stored on data blocks of different HDs respectively, The method comprises the steps of reading super blocks of all of the HDs; comparing the number of the HDs and time being involved in a previous operation and stored in the super blocks with each other; reading common data involved in the previous degraded operation of the RAID; writing the read common data into the super blocks of all of the HDs; and recovering a configuration of the RAID to the degraded mode again.