Disk Array Control Lost Write Recovery via Data Comparison
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Solution Overview
Problem
Conventional disk array systems with RAID level redundant configuration face issues with lost writes during error recovery, where data redundancy cannot be recovered due to incorrect rewriting of data at different addresses, leading to inconsistencies between primary and secondary disk apparatuses.
Innovation Solution
A two-stage recovery processing method is implemented, where the first stage involves reading and writing data from a normal disk apparatus to correct errors, and the second stage retrieves and writes correct data from the normal apparatus to the error disk based on mismatched identifiers, ensuring data consistency and recovering redundancy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional patrol processing is used to detect errors in disk apparatuses, then errors can be detected and basic recovery processing can be performed, but lost writes occur where data redundancy cannot be recovered due to incorrect rewriting of data at different addresses
Solution Approach 1:
The recovery processing is divided into two distinct stages: first recovery processing for basic error correction, and second recovery processing for lost write detection and correction. This segmentation allows the system to handle different types of errors appropriately, preventing lost writes while maintaining data redundancy.
Solution Approach 2:
The system uses feedback from patrol processing to trigger appropriate recovery actions. When an error is detected during patrol processing, the system feeds back control to perform first recovery processing, then checks for lost writes through second recovery processing, ensuring complete error correction and redundancy restoration.
2Reliability
If first recovery processing is performed to correct errors by reading data from normal disk apparatus, then errors can be eliminated, but lost writes remain unresolved where data consistency cannot be recovered
Solution Approach 1:
The recovery process is segmented into two phases: first recovery processing handles basic error correction, while second recovery processing specifically addresses lost writes by comparing data between disk apparatuses and correcting inconsistencies, thereby restoring data consistency.
Solution Approach 2:
The system replaces simple mechanical data copying with a more sophisticated process that includes comparison and verification steps. The second recovery processing uses comparison logic to detect lost writes and targeted writing to correct them, ensuring data consistency is restored.
3Productivity
If simple error recovery processing is used, then the recovery process is simple and fast, but data redundancy is lost and cannot be recovered
Solution Approach 1:
The recovery processing is segmented into two stages that can be executed sequentially. The first stage performs basic error correction quickly, while the second stage performs lost write detection and correction only when necessary, maintaining overall efficiency while ensuring complete data redundancy recovery.
Solution Approach 2:
The system performs partial recovery actions in the first stage (basic error correction) and only performs the additional second stage actions (lost write detection and correction) when needed, optimizing the balance between recovery speed and completeness.
Data Source
AI summary
When receiving a notification of an error detected by patrol processing of the device adaptor for a secondary disk apparatus, a first recovery processing unit reads out data corresponding to the error location from a normal primary disk apparatus and writes the data into the error disk apparatus to eliminate the error. If it is determined that the content of the error notification is abnormality of the block ID which is an identifier of the order of writing data, a second recovery processing unit retrieves a correct write address indicated by the identifier, compares data of the error disk apparatus with that of the normal disk apparatus, determines that a lost write exists in the case of mismatch, and eliminates the lost write by writing the data read out from the normal disk apparatus into the error disk apparatus.