Point-in-Time Copy Consistency via Flush Coordination
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Solution Overview
Problem
Existing communication protocols fail to coordinate a consistent point-in-time copy of datasets across storage nodes and client devices, leading to potential inconsistencies in data capture.
Innovation Solution
A system and method that involves a data provider instructing clients and servers to flush pending updates, acknowledging completion, and using a write-aside buffer to defer post-consistency updates, ensuring a consistent dataset snapshot is taken.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing communication protocols are used for point-in-time copy operations, then the copy operation can be performed, but data consistency between storage nodes and client devices cannot be ensured
Solution Approach 1:
The system performs preliminary actions by sending flush requests to all client devices before capturing the point-in-time copy. This ensures that all pending writes are committed to storage before the snapshot is taken, guaranteeing data consistency without requiring complex coordination during the actual copy operation.
Solution Approach 2:
The system implements feedback mechanisms where client devices acknowledge receipt of flush requests and confirm when their pending writes have been committed. The storage node tracks these acknowledgments and only proceeds with the point-in-time copy when all necessary clients have confirmed their data is flushed, ensuring consistency through verifiable feedback.
2Reliability
If the dataset is frozen to prevent updates during point-in-time copy, then data consistency is improved, but system productivity and access continuity deteriorate
Solution Approach 1:
The system performs the consistency-ensuring flush operation before the point-in-time copy is initiated. This preliminary action captures all pending writes to storage, allowing the subsequent copy operation to read from a consistent state without freezing the live dataset or interrupting client access continuity.
Solution Approach 2:
The system separates the consistency assurance mechanism (flush operations) from the copy operation itself. By segmenting these functions and executing the flush phase independently before the snapshot phase, the system maintains data consistency while allowing the dataset to remain accessible and mutable during the copy process.
3Reliability
If flush requests are sent to all clients before point-in-time copy, then data consistency is improved, but the time required for the copy operation increases
Solution Approach 1:
The system leverages the client devices' existing write-back caching mechanisms and flush capabilities. Instead of the storage node performing complex data gathering operations, each client device independently flushes its own pending writes to storage using its native protocols, significantly reducing the coordination overhead and time required.
Solution Approach 2:
The flush requests are sent in advance and can be processed in parallel across multiple client devices simultaneously. This preliminary action allows the system to initiate the consistency assurance process early, and while waiting for clients to flush, the storage node can prepare for the copy operation, overlapping useful work to minimize total time.
Data Source
AI summary
A system and method for facilitating a consistent point-in-time copy (PITC). A data provider offers access to data by one or more clients. A client issues a PITC request for a set of data to the data provider, or the provider initiates its own request. The data provider instructs one or more clients, particularly clients accessing the set of data, to flush any pending updates involving the files. The clients acknowledge the flush request, flush their data, and notify the data provider when their flushes are complete. Post-consistency updates are deferred (e.g., using a write-aside buffer). If a client fails to acknowledge the flush request or notify of flush completion, the data provider may abort the PITC or continue because the data may not be consistent or consistency may not be assured. If not aborted, the PITC may be marked to indicate that it is incomplete.