Active/Active Remote Mirroring for Clustered Storage
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Solution Overview
Problem
Current data replication and mirroring systems face issues with latency in synchronous transfers, data consistency in asynchronous transfers, and active/passive operational behavior, which are inadequate for clustered applications requiring symmetric storage and high availability.
Innovation Solution
An active/active mirroring system is implemented, where both storage devices are accessible for I/O operations and control mirroring operations synchronously with host I/O, allowing for automatic failover and lock conflict resolution, ensuring data consistency and high availability without the need for explicit failover or server mirroring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If synchronous RDF transfer is used to ensure data consistency between primary and secondary storage devices, then data consistency is improved, but latency is increased due to waiting for acknowledgment
Solution Approach 1:
The system performs preliminary actions by having the primary storage device send data to the secondary storage device before receiving acknowledgment. The write operation is considered complete once the secondary device acknowledges receipt, allowing the host to proceed without waiting for full synchronization confirmation, thus reducing latency while maintaining data consistency.
Solution Approach 2:
The system dynamically adjusts the synchronization behavior based on operational conditions. During normal operation, synchronous transfer ensures consistency, but the system can transition to asynchronous operation when latency becomes problematic, allowing flexible optimization between consistency and performance based on real-time needs.
2Loss of time
If asynchronous background copy is used to reduce latency, then latency is improved, but data consistency cannot be guaranteed between primary and secondary storage devices
Solution Approach 1:
The system implements feedback mechanisms where the secondary storage device sends acknowledgment signals back to the primary device to confirm successful data receipt. This feedback loop allows the system to verify data consistency without requiring the host to wait, as the acknowledgment process occurs in the background while providing confirmation that consistency has been maintained.
3Device complexity
If active/passive operational behavior is used in RDF systems, then device complexity is reduced, but adaptability is decreased for clustered applications requiring symmetric storage
Solution Approach 1:
The system implements multi-functionality by enabling both storage devices to operate in active roles simultaneously. Each device can serve as a primary device for different hosts or data sets, providing universal active/active capability that supports clustered applications and symmetric storage requirements while maintaining manageable complexity through standardized protocols.
4Reliability
If synchronous RDF transfer is used over long distances, then data consistency is improved, but transmission delays are increased making the transfer time undesirable
Solution Approach 1:
The system performs preliminary data transfer actions over the long-distance connection before the host completes its write operation. By initiating the transfer in advance and using acknowledgment-based completion, the system reduces the perceived transfer time for the host while ensuring data consistency is maintained through the acknowledgment protocol.
Data Source
AI summary
An active/active remote mirroring system, for example an active/active SRDF system, provides for remote mirroring between multiple storage volumes, e.g., a first storage device and a second storage device, in which the storage devices may both be active. A plurality of hosts may be coupled to either the first storage device, the second storage device, or both to conduct read and write operations from and to the storage devices, for example to nearest device. The hosts may be part of an application cluster. The first storage device and the second storage device may be connected via a link, such as an SRDF link, for providing remote mirroring capabilities between the storage volumes. In various embodiments the first and second storage devices may be separate devices, volumes, or portions thereof, and/or may be different portions of the same storage device.