Dual-Server Cache Data Preservation via Preemptive Retrostore
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Solution Overview
Problem
In dual-server storage systems, there is a risk of data loss during failover due to the time-consuming process of destaging data from cache to secondary storage, which can be exacerbated by power failures or unavailability of secondary storage devices, leading to potential data loss in minutes or more.
Innovation Solution
Implementing a preemptive retrostore mechanism that transfers data from cache to non-volatile storage (NVS) of an operational server if space is available, thereby reducing the window of potential data loss and ensuring data protection against power failures or destage operation failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If data is kept in cache during failover, then data access speed is improved, but data loss risk increases due to power failures or destage operation failures
Solution Approach 1:
The system performs preliminary action by proactively transferring data from cache to non-volatile storage before a failover event occurs. The retrostore mechanism continuously monitors cache data and preemptively persists it to NVS, ensuring data is protected before any potential power failure or destage operation failure can occur.
Solution Approach 2:
The system applies beforehand cushioning by maintaining a protective buffer through the retrostore mechanism. This mechanism creates a safety cushion by continuously copying cache data to non-volatile storage, providing a protective layer against data loss from power failures or destage operation failures.
2Reliability
If data is transferred to non-volatile storage during failover, then data protection is improved, but data loss window reduction is achieved
Solution Approach 1:
The retrostore mechanism ensures continuity of useful action by continuously transferring data from cache to non-volatile storage without interruption. This continuous operation minimizes the window of vulnerability by ensuring data is constantly protected, reducing the time gap between data modification and its protected state.
Solution Approach 2:
The system applies skipping by rapidly transferring data from cache to non-volatile storage during failover events. This rushed transfer through the retrostore mechanism quickly reduces the data loss window by swiftly persisting protected copies before failures can occur.
3Reliability
If dual-server configuration is used, then system availability is improved, but complexity of data management increases
Solution Approach 1:
The system merges data management functions by combining the retrostore mechanism across both servers in the dual-server configuration. This unified approach consolidates data protection operations, reducing management complexity while maintaining high availability through coordinated failover capabilities.
Solution Approach 2:
The retrostore mechanism provides universality by serving multiple functions: it protects data during normal operation, facilitates failover between servers, and provides recovery capabilities. This multi-functional approach simplifies data management in dual-server configurations by using a single mechanism for multiple protection scenarios.
Data Source
AI summary
A dual-server based storage system maintains a first cache and a first non-volatile storage (NVS) in a first server, and a second cache and a second NVS in a second server, where data in the first cache is also written in the second NVS and data in the second cache is also written in the first NVS. In response to a failure of the first server, a determination is made as to whether space exists in the second NVS to accommodate the data stored in the second cache. In response to determining that space exists in the second NVS to accommodate the data stored in the second cache, the data is transferred from the second cache to the second NVS.