Remote Storage Replication with Local Cache Write Acknowledgment
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Solution Overview
Problem
Synchronous remote replication in storage systems experiences significant delays due to long distances between primary and remote storage devices, leading to increased latency in write response times.
Innovation Solution
The primary storage device writes data to its cache and interface card before sending a write success response to the host, allowing it to send data to the remote storage device independently, thus reducing synchronization delays and improving data reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the primary storage device waits for remote storage confirmation before sending write success response, then data consistency between primary and remote storage is ensured, but write response delay increases significantly
Solution Approach 1:
The primary storage device performs preliminary local caching of target data before remote replication. The write success response is sent to the host after local cache confirmation, while remote replication continues in the background. This preliminary local action ensures data consistency without waiting for remote confirmation, resolving the contradiction between reliability and response delay.
Solution Approach 2:
The data replication process is segmented into independent stages: local cache writing and remote replication. These stages are decoupled so that the write success response can be sent after local completion without waiting for remote completion. This segmentation allows the system to maintain data consistency while reducing the critical path delay.
2Loss of time
If the primary storage device sends write success response immediately after local caching, then write response delay is reduced, but data consistency with remote storage cannot be guaranteed
Solution Approach 1:
The primary storage device's cache acts as an intermediary between the host and remote storage. The cache holds data temporarily, allowing the host to receive immediate write confirmation while the cache simultaneously forwards data to remote storage. This intermediary mechanism decouples the host response timing from remote replication timing, reducing delay while maintaining consistency.
3Reliability
If synchronous remote replication is implemented over long distances, then disaster recovery capability is improved, but synchronization duration increases
Solution Approach 1:
Data is preliminarily cached locally at the primary storage device before being transmitted to remote storage. This preliminary local storage ensures that disaster recovery capability is maintained through local data availability, while the actual remote transmission can proceed asynchronously without blocking host operations, thereby reducing synchronization duration impact.
Data Source
AI summary
A synchronous remote replication method and apparatus for a storage system are provided. The storage system includes a primary storage device and a remote storage device. The primary storage device includes a cache and a primary interface card. One example method includes: the primary storage device obtaining the host's write request with target data; writing the target data into the primary interface card and cache; sending a write success response to the host upon successful cache writing; and transmitting the target data to the remote storage device upon successful primary interface card writing.