Asynchronous Snapshot Rollback Using Differential Bitmaps
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Solution Overview
Problem
In data replication systems, rolling back snapshots during asynchronous replication can disrupt storage systems due to the need to terminate replication sessions and result in lost time, especially when previous point-in-time snapshots are not readily available at the source storage system.
Innovation Solution
A method and system for performing rollback of snapshots between a source and target storage system in an asynchronous replication session by suspending host I/O operations, determining the presence of matching snapshots, searching for the closest snapshot pair, and applying differences using a snapshot differential bitmap for local and remote rollback without terminating replication sessions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If previous point-in-time snapshots are stored in remote storage system due to capacity limits at source, then snapshot retention is improved, but rollback complexity increases
Solution Approach 1:
The patent introduces an intermediary mechanism consisting of snapshot metadata stored at the source system and differential bitmaps stored at the remote system. This intermediary structure enables the source system to initiate rollbacks to remote snapshots without requiring direct access to the actual snapshot data, thereby reducing rollback complexity while maintaining improved snapshot retention.
Solution Approach 2:
The rollback process is segmented into distinct phases: (1) metadata verification at source, (2) differential bitmap application at source, and (3) data synchronization with remote system. This segmentation allows each component to be optimized independently, reducing overall complexity while enabling extended snapshot retention across distributed systems.
2Adaptability or versatility
If replication session is terminated during rollback activities, then rollback capability is improved, but productivity deteriorates
Solution Approach 1:
The patent implements a dynamic replication session management system that can operate in multiple modes: suspended mode during rollback operations and active mode for normal replication. The system dynamically transitions between these modes based on operational requirements, allowing rollback capability to be exercised without permanently terminating the replication session, thereby maintaining productivity.
Solution Approach 2:
The system performs preliminary actions by pre-storing snapshot metadata and differential bitmaps before rollback is needed. This preliminary preparation allows the actual rollback operation to proceed quickly without requiring full session termination, as the necessary data structures are already in place and can be applied incrementally.
3Speed
If local rollback is performed using snapshot pair from existing snapsets, then rollback speed is improved, but snapshot availability worsens
Solution Approach 1:
The patent implements a nested snapshot architecture where local snapsets contain recently accessible snapshots for fast rollback, while remote storage systems contain historical snapshots for extended availability. The system nests these two layers, allowing the source system to quickly access local snapshots when available while automatically falling back to remote snapshots when needed, thereby achieving both fast rollback speed and comprehensive snapshot availability.
Data Source
AI summary
An aspect of performing rollback of a snapshot between source and target storage systems in an asynchronous replication session in which Sr′ represents a remote snapshot subject to the rollback includes suspending host input/output operations to a current source volume (Vs), determining whether a snapshot (Sr) matching the snapshot Sr′ is present in the source system and, upon determining the snapshot Sr is not present in the source storage system, searching a snapshot pair (Sk, Sk′) that is closest to the remote snapshot Sr′. An aspect also includes upon determining the pair Sk, Sk′ is present in existing snapsets, performing a local rollback of the Vs to Sk, and performing remote rollback including applying a difference between Sk′ and Sr′ to the Vs via one of a snapshot differential bitmap from the target storage system between Sk′ and Sr′ for the Vs, and an internal reverse direction asynchronous replication cycle.