Persistent Cache for Degraded Disk Array Write Consistency
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Solution Overview
Problem
In a storage system with a disk array in degraded mode, existing methods face challenges in ensuring data consistency during write operations, leading to increased response times and wear on storage disks, particularly when using flash memory drives.
Innovation Solution
The implementation of a method that uses a high-speed cache component with persistent memory to replace the conventional journal writing procedure, allowing new data and parity information to be written into cache pages and subsequently flushed to the disk array, thereby reducing the number of disk reads and writes and ensuring data consistency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional journal writing procedure is used in degraded mode, then data consistency can be ensured, but response time increases and disk wear increases
Solution Approach 1:
The patent introduces a cache component as an intermediary between the host and disk array. The cache stores old data and old parity information, allowing the system to retrieve these values quickly without reading from the degraded disk array during write operations. This mediator resolves the contradiction by providing fast access to necessary data while the actual disk operations proceed separately.
Solution Approach 2:
The system performs preliminary actions by pre-reading old data and old parity information into the cache before processing write requests. By having these values readily available in the cache component, the system avoids time-consuming disk reads during the critical write path, thus reducing response time while maintaining data consistency through proper parity recalculation.
2Reliability
If conventional journal writing procedure is used in degraded mode, then data consistency can be ensured, but the number of disk operations increases
Solution Approach 1:
The cache component serves as a mediator that handles data and parity information storage temporarily. Instead of repeatedly reading from and writing to the degraded disk array during write operations, the cache intermediates these operations, reducing the total number of disk reads and writes while ensuring data consistency through proper cache management and flush operations.
Solution Approach 2:
The system creates copies of old data and old parity information in the cache component. These copies are used for processing write requests without requiring additional reads from the original disk array. This copying mechanism reduces disk operations while maintaining the integrity needed for data consistency.
3Speed
If flash memory drives are used, then write speed improves, but wear from frequent operations reduces service life
Solution Approach 1:
The cache component acts as a buffer that absorbs frequent write operations. By storing old data and parity information in the cache, the system minimizes the need for repeated flash memory read/write cycles on the disk array. This intermediary approach allows flash memory to operate at high speeds when necessary while reducing overall wear and extending service life.
Data Source
AI summary
Embodiments of the present disclosure relate to methods, devices and computer program products for writing data in a disk array in a storage system. The storage system comprises a disk array. The method comprises: in response to receiving a write request to write new data to a data block in at least one disk array group in a degraded mode within a disk array, reading old data stored in the data block and old parity information stored in a parity block associated with the data block. The method further comprises: determining new parity information associated with the new data based on the old data, the old parity information and the new data. The method further comprises: writing the new data and the new parity information into at least one cache page provided by a cache component in the storage system, the at least one cache page being allocated in a persistent memory in the cache component. In addition, this method further comprises: flushing the new data and the new parity information into the data block and the parity block in the at least one disk array group, respectively.