Storage Migration Journal Consistency During Asynchronous Copy
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Solution Overview
Problem
Existing remote copy systems face challenges in migrating a primary logical volume (PVOL) from an old model storage apparatus to a new model without additional functionality on the source storage apparatus, especially during asynchronous remote copying, where journal management between the source and destination is inconsistent.
Innovation Solution
The solution involves coupling a migration-destination primary storage apparatus to a migration-source primary storage apparatus, where the destination apparatus stores journals corresponding to write data and updates, using latest write sequence information to ensure consistency, and manages journal storage areas within the storage controller or memory.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If asynchronous remote copying is performed during migration, then data consistency is maintained, but journal management becomes inconsistent between source and destination
Solution Approach 1:
The patent introduces a journal transfer mechanism where the source storage apparatus acts as an intermediary to transfer journals to the destination storage apparatus during migration. This mediator approach allows asynchronous remote copying to continue while maintaining consistent journal management, as the destination apparatus receives and processes journals from the source rather than attempting to manage them independently.
Solution Approach 2:
The patent implements preliminary journal transfer before completing the migration process. By transferring journals from the source to the destination storage apparatus in advance and during the migration process, the system ensures that the destination is prepared to handle asynchronous remote copying operations immediately upon migration completion, preventing journal management inconsistencies.
2Device complexity
If migration is performed without additional functions on source storage apparatus, then system simplicity is maintained, but migration capability is limited
Solution Approach 1:
The patent enables the source storage apparatus to perform multiple functions: it serves as both the original storage device and a journal transfer mechanism during migration. The destination storage apparatus similarly performs multiple roles including receiving data, receiving journals, and immediately becoming operational for asynchronous remote copying. This multi-functionality allows migration without adding specialized migration hardware or software.
Solution Approach 2:
The migration process is designed to be self-service in that the destination storage apparatus automatically begins receiving and processing journals from the source during the migration process, and immediately upon completion, the destination can independently handle asynchronous remote copying operations without requiring additional configuration or functions on the source apparatus.
3Productivity
If journal transfer is performed during ongoing asynchronous remote copying, then seamless migration is achieved, but synchronization challenges arise
Solution Approach 1:
The patent implements a feedback mechanism where the destination storage apparatus receives journals from the source storage apparatus during migration and processes them in sequence. The journal transfer is synchronized with the ongoing asynchronous remote copying operations, ensuring that data and journal updates remain consistent. The destination uses the received journals to maintain proper synchronization state without losing information.
Data Source
AI summary
A migration-destination primary storage apparatus (MD-PDKC) comprises a second PVOL and a second journal storage area storing a journal corresponding to write data for the second PVOL, and executes a data copy to the second PVOL from a first PVOL, which is in a migration-source primary storage apparatus (MS-PDKC) and forms a copy pair with an SVOL in a secondary storage apparatus (SDKC). After the data copy has been completed, the MD-PDKC acquires the latest write sequence information from the MS-PDKC, and upon receiving a write request for the second PVOL, writes the write-request write data to the second PVOL, creates a journal by using journal data corresponding to the write data and also by using update information showing write sequence information based on the acquired latest write sequence information, and writes the journal to the second journal storage area.