Flash Cache Asynchronous Remote Copy Processor Load Reduction
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Solution Overview
Problem
The existing asynchronous remote copy systems face increased processor load due to the need to manage journal data and update data in cache memory, particularly when using DRAM, which requires either evacuating old data or storing journal data, leading to inefficiencies and increased load on the processor.
Innovation Solution
A storage system utilizing a flash package with a package processor that allocates physical areas for write data and journal data separately, allowing for efficient storage and management without overwriting old data, thereby reducing processor load and improving response performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If DRAM cache memory is used for storing write data and journal data, then fast write performance is achieved, but processor load increases due to the need to evacuate old data or manage journal data separately
Solution Approach 1:
The patent combines the storage of write data and journal data into the same flash memory cache area. When write data is stored in the cache, it is automatically managed as journal data without requiring separate storage management. This merging eliminates the need for the processor to evacuate old data or manage separate journal data areas, thereby reducing processor load while maintaining fast write performance through flash memory caching.
Solution Approach 2:
The flash memory cache serves multiple functions simultaneously: it acts as both write data cache and journal data storage. The same physical cache area is used for both purposes, with the flash memory package processor managing the dual functionality. This multi-functionality reduces the overall system complexity and processor overhead compared to using separate cache areas for write data and journal data.
2Ease of operation
If separate storage areas are allocated for write data and journal data in cache memory, then data management is simplified, but storage capacity requirements increase
Solution Approach 1:
The patent merges the storage areas for write data and journal data into a single flash memory cache space. The flash memory package processor manages this unified area, allocating space dynamically between write data and journal data as needed. This approach reduces total storage capacity requirements compared to maintaining separate dedicated areas, while the package processor maintains simplified data management through automatic tracking of write operations and their corresponding journal data.
3Speed
If DRAM cache is used with overwrite capability, then write speed is improved, but journal data may be accidentally erased by update write processes
Solution Approach 1:
The patent converts the flash memory's overwrite limitation into a benefit for journal data integrity. Since flash memory cannot overwrite existing data, the system automatically preserves old data when new write operations occur. This characteristic, which might be seen as a limitation, actually prevents accidental erasure of journal data and eliminates the need for complex data evacuation processes required by DRAM systems.
Solution Approach 2:
The flash memory's inherent non-overwrite characteristic automatically protects journal data from being erased by update operations. The system does not need to implement active protection mechanisms or data evacuation processes; the physical property of flash memory itself provides the protection. This self-service approach enhances journal data integrity while maintaining write speed through the caching mechanism.
Data Source
AI summary
The first storage apparatus provides a primary logical volume, and the second storage apparatus has a secondary logical volume. When the first storage apparatus receives a write command to the primary logical volume, a package processor in a flash package allocates first physical area in the flash memory chip to first cache logical area for write data and stores the write data to the allocated first physical area. And when the package processor receives journal data creation command form the processor, allocates the first physical area to second journal area for journal data without storing journal data corresponding to the write data.