Host Cache Snapshot Coordination for SAN Data Consistency
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Solution Overview
Problem
Current storage area networks (SANs) face challenges in efficiently managing snapshots and data replication across distributed locations, particularly in ensuring data consistency and availability during server failures and disaster recovery processes.
Innovation Solution
The integration of a host cache system with a SAN plugin that coordinates snapshot creation and access, utilizing virtual IP addresses and cache modes like write-back and write-thru to ensure data integrity and availability, allowing for seamless data replication and recovery across multiple SAN instances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a host cache system is integrated with SAN to improve data access speed, then productivity is improved, but data consistency and reliability may deteriorate due to potential data loss in cache during server failures
Solution Approach 1:
The system performs preliminary actions by creating snapshots of cache data before potential failures occur. The snapshot coordinator proactively captures cache state at specific points in time, ensuring that even if the cache is lost during a server failure, the data can be recovered from the snapshot, thus maintaining both speed and reliability
Solution Approach 2:
The invention creates copies of cache data in the form of snapshots stored on SAN. These snapshots serve as redundant copies that can be used for recovery purposes, allowing the system to maintain fast cache access while having backup copies available to ensure data consistency in case of failures
2Duration of action of stationary object
If snapshots are stored in the cache to enable quick recovery, then duration of action is improved, but device complexity increases due to coordination requirements between SAN and cache
Solution Approach 1:
The snapshot coordinator acts as an intermediary component that manages snapshot operations between the SAN and cache. It coordinates snapshot creation, storage, and retrieval without requiring complex direct coordination between SAN and cache systems, thereby simplifying the overall system architecture while enabling fast recovery
Solution Approach 2:
The snapshot management functionality is segmented into a separate coordinator component rather than being embedded within the SAN or cache systems. This segmentation allows each component to maintain its simplicity while the coordinator handles the coordination logic, reducing overall device complexity
3Productivity
If write-back cache mode is used to improve writing speed, then productivity is improved, but loss of information increases if power fails before data is flushed to SAN
Solution Approach 1:
The system performs preliminary snapshot actions at configured intervals or before critical operations. This ensures that even if power fails during write-back cache operations, the most recent snapshot captures the data state, limiting information loss to only the changes made after the snapshot was taken
Solution Approach 2:
The snapshot mechanism provides beforehand cushioning by creating protective data copies before potential failures occur. These snapshots act as a cushion against data loss, allowing the system to use aggressive write-back caching while having pre-established safety nets to recover from power failures
Data Source
AI summary
In one embodiment, a method performed by one or more computing devices includes receiving at a host cache a first request for data comprising at least one snapshot of a cached logical unit number (LUN), sending, by the host cache, the data comprising at least one snapshot of the cached LUN in response to the first request, and in response to the completing sending the data comprising at least one snapshot of the cached LUN, sending, by the host cache, a first response indicating that sending the data is complete.