Storage Replication Mode Transition via Snap Set Pairs
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Solution Overview
Problem
Switching between different replication modes in storage systems, such as synchronous, asynchronous, and metro replication, is challenging due to the need for distinct preconditions and potential disruptions during transitions, which can result in complex switch flows and increased latency or data lag.
Innovation Solution
A framework is provided that identifies generic functions common to all replication modes and adjusts for custom functions specific to each mode, allowing for seamless transitions by validating preconditions, suspending data flow, establishing base snap sets, updating snap sets on both source and target systems, and implementing mode transition cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If distinct preconditions and complex switch flows are implemented for each replication mode transition, then mode switching capability is achieved, but system complexity and latency increase
Solution Approach 1:
The patent implements a universal mode transition framework that handles all replication mode transitions (sync-to-async, async-to-sync, metro-to-async, etc.) through a single standardized process. The framework uses common elements like base snap set pairs, mode transition cycles, and precondition validation that work across all mode combinations, eliminating the need for separate switch flows for each mode transition type.
Solution Approach 2:
The transition process is segmented into distinct manageable phases: validating preconditions, suspending data flow, establishing base snap set pairs, updating snap sets on source and target systems, implementing mode transition cycles, and resuming data flow. This segmentation allows each phase to be optimized independently while maintaining overall simplicity.
2Ease of manufacture
If mode transition processes are simplified, then development and testing efforts are reduced, but data protection and system performance may be compromised
Solution Approach 1:
The framework performs preliminary actions before mode transition by validating preconditions (ensuring target system is ready), suspending data flow (preventing new writes during transition), and establishing base snap set pairs (creating reference points for consistent state). These preliminary actions ensure data protection is built into the transition process before it begins, rather than added as an afterthought.
Solution Approach 2:
The patent introduces intermediary structures including base snap set pairs and mode transition cycles that mediate between the source and target systems during transition. These intermediaries coordinate the complex state changes and snap set updates, ensuring consistent data protection across all replication modes while simplifying the overall transition logic.
3Reliability
If data flow is suspended during mode transition, then data protection is ensured, but latency and data lag increase
Solution Approach 1:
The framework maintains continuity of useful action by using asynchronous snap set updates and mode transition cycles that can proceed in parallel where possible. The base snap set pairs are established and updated concurrently on source and target systems, and the mode transition cycles are implemented to minimize interruption time. Data flow suspension is limited only to the critical transition window, not the entire operation.
Solution Approach 2:
The system changes operational parameters during transition by switching between different replication modes (synchronous, asynchronous, metro) which have different latency characteristics. The framework leverages the faster asynchronous mode during transition periods when possible, and only suspends data flow during the brief window when consistency must be maintained, thereby minimizing overall latency impact.
Data Source
AI summary
In one aspect, transitioning among replication modes in a storage system is provided. An aspect includes during an active replication session in which a first replication mode is performed, validating a precondition for transitioning to a second replication mode that is different from the first mode of replication. An aspect further includes suspending data flow for the active session, establishing a base snap set pair for a mode transition cycle, and preparing for the transitioning including updating, for the mode transition cycle, the base snap set pair on both a source system and a target system of the storage system, and creating a snap set against an active snap set on the target system as a mode transition cycle snap set. An aspect further includes implementing the mode transition cycle, and entering a replication session, upon completion of the mode transition cycle, for the second mode of replication.