Snapshot Rollback in Synchronous Replication Without Session Halt

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Solution Overview

Problem

Conventional data replication methods, particularly synchronous replication, face challenges in rolling back snapshots without terminating and restarting the replication session, leading to lengthy data protection windows when large amounts of data are involved.

Innovation Solution

The method involves reassigned current replication source volumes to a rollback source snapshot, performing differential scans, calculating dirty tree differentials, and initiating copy commands to translate metadata requests for efficient rollback during ongoing synchronous replication sessions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If synchronous replication session is halted and restarted to perform snapshot rollback, then rollback operation can be completed, but data protection window gap increases and productivity decreases

Engineering Contradiction:

Improvesnapshot rollback accuracyVSAvoiddata protection window

Core Design Contradiction:

Manufacturing precisionVSProductivity

Solution Approach 1:

The system performs preliminary actions by creating a new child snapshot before the rollback operation and pre-calculating the differential scan results. This allows the replication session to continue without interruption while the rollback is prepared and executed in the background, eliminating the need to halt the session for rollback operations.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The rollback operation is segmented into independent steps: creating a child snapshot, performing differential scan, identifying dirty pages, and copying data. This segmentation allows each step to be executed independently without interrupting the overall replication session, maintaining continuous data protection while completing the rollback.

Inventive Principle:

Principle #1Segmentation

2Manufacturing precision

If synchronous replication session is halted for snapshot rollback, then rollback can be performed, but time consumption increases

Engineering Contradiction:

Improvesnapshot rollback accuracyVSAvoiddata protection window gap

Core Design Contradiction:

Manufacturing precisionVSLoss of time

Solution Approach 1:

The replication session maintains continuous operation during the rollback process. The system uses differential scanning to identify only the changed pages (dirty pages) between the source snapshot and rollback snapshot, copying only these specific pages rather than retransmitting the entire volume. This continuous action approach minimizes time consumption while ensuring accurate rollback.

Inventive Principle:

Principle #20Continuity of useful action

3Reliability

If large quantity of data is retransmitted after session restart, then data consistency is restored, but productivity decreases and time loss increases

Engineering Contradiction:

Improvedata consistencyVSAvoiddata protection window

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The system extracts only the necessary data for rollback by performing a differential scan that identifies specifically which pages have changed between the current snapshot and the rollback target snapshot. Only these extracted dirty pages are copied to the target system, rather than retransmitting the entire large quantity of data, thus maintaining data consistency while improving productivity.

Inventive Principle:

Principle #2Taking out (Extraction)

4Manufacturing precision

If synchronous replication session is halted and restarted, then snapshot rollback is completed, but device complexity increases

Engineering Contradiction:

Improvesnapshot rollback accuracyVSAvoidreplication session management

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The system performs preliminary setup by creating a child snapshot structure before the rollback operation begins. This preliminary action establishes the necessary data structures and relationships, allowing the rollback to proceed smoothly without complex session halting and restarting procedures, thus reducing overall system complexity while maintaining accurate rollback functionality.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS11386124B2Snapshot rollback for synchronous replication

Publication Date: 2022.07.12 DELL PROD LP

AI summary

An aspect of performing rollback of a snapshot between a source storage system and a target storage system in a synchronous replication session includes reassigning a current replication source volume to a rollback source snapshot. The rollback source snapshot is generated for a consistency group that includes a plurality of volumes. An aspect also includes performing, for one or more snapshot trees maintained for the consistency group, a differential scan between a child of the rollback source snapshot and the current replication source volume, and calculating, from results of the differential scan, a dirty tree differential. For each difference identified in the dirty tree differential, an aspect further includes calculating a corresponding volume offset, and initiating a copy command for the current replication source volume and the rollback source snapshot. The copy command is translated to a remote metadata copy request in synchronous replication data transfer.