Dual-Copy Cross-Site Storage with Primary-First Conflict Ordering

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Solution Overview

Problem

Fully symmetric storage solutions in dual copy multi-site distributed data storage systems face challenges in maintaining data and metadata consistency during bidirectional replication, leading to inconsistencies and deadlocks due to unserialized dependent operations.

Innovation Solution

Implement bi-directional synchronous replication with a primary-first principle, using an overlap write manager lock and suspending conflicting operations to ensure consistent data and metadata handling across primary and secondary storage sites.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If locks are used to achieve serialization of dependent operations, then data consistency is improved, but deadlocks occur and system availability deteriorates

Engineering Contradiction:

Improvedata consistencyVSAvoidsystem availability

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent assigns a primary site and secondary site roles beforehand, establishing a predetermined order of operations. The primary site always executes operations first, and the secondary site replicates them in the same order. This preliminary assignment prevents deadlocks by eliminating the need for dynamic lock negotiation between sites.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Instead of using locks to prevent conflicts (the conventional approach), the patent inverts the problem by using role-based operation ordering. The primary site and secondary site are given asymmetric rights to execute operations, with the primary site having priority. This inversion transforms a synchronization problem into a hierarchical execution model.

Inventive Principle:

Principle #13The other way round (Inversion)

2Adaptability or versatility

If bidirectional simultaneous read-write access is enabled, then system versatility is improved, but data divergence occurs and reliability deteriorates

Engineering Contradiction:

Improvesimultaneous read-write accessVSAvoiddata consistency

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent segments the write operation authority by site role. The primary site is authorized to initiate write operations, while the secondary site is authorized only to replicate them. This segmentation of operational authority allows simultaneous reads at both sites while preventing write conflicts that would cause data divergence.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces asymmetry in the replication relationship by designating one site as primary and the other as secondary. Although both sites can perform reads, write operations follow an asymmetric path: primary site writes first, then secondary site replicates. This asymmetric write protocol maintains consistency while allowing symmetric read access.

Inventive Principle:

Principle #4Asymmetry

3Productivity

If dependent operations are executed in parallel without serialization, then productivity is improved, but data consistency deteriorates and operational conflicts arise

Engineering Contradiction:

Improveoperation throughputVSAvoiddata consistency

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent establishes a preliminary execution order through site role assignment before operations begin. The primary site is predetermined to execute operations first, and the secondary site is predetermined to replicate them afterward. This preliminary ordering enables parallel execution of independent operations while maintaining consistency for dependent operations.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS20260030216A1Systems and methods to handle dependent data, conflicting data, or metadata operations on a dual copy cross-site storage system with simulataneous read-write ability on each copy

Publication Date: 2026.01.29 NETAPP INC

AI summary

The present storage solution provides an order of operations of a computer-implemented method that includes implementing a primary-First principle with a first data Op received by the primary storage site being executed on the primary storage site and then replicated to the secondary storage site and a second data Op received by the secondary storage site being first replicated to the primary storage site. The method further includes acquiring overlap write manager (OWM) lock locally on the primary storage site for the first data Op if there are no conflicting ops that are already inflight working on an overlapping range, sending the first data Op to a file system of the primary storage site to modify the file system as per primary-first principle, and suspending any new Ops from the primary storage site that have an overlapping range that overlaps with a range of the first data Op.