Asynchronous Storage Timestamp File for Write Time Determination
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Solution Overview
Problem
Existing data transfer mechanisms, such as SRDF/A, do not allow for the precise determination of data write times at a remote storage system during asynchronous data replication, which is crucial for applications requiring host data write time information.
Innovation Solution
A system that maintains a timestamp file at the local storage system, where each chunk of data is assigned a sequence number, and the timestamp file is transferred independently to the remote storage system, allowing for the correlation of cycle numbers with timestamp files to determine the write time of specific data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If asynchronous data transfer is used to replicate data from primary to secondary storage system, then data transfer flexibility and independence are improved, but the ability to determine specific write times at the remote storage system deteriorates
Solution Approach 1:
The system performs preliminary actions by capturing the host write time at the primary storage system before data is transferred asynchronously to the secondary storage system. This timestamp is recorded in advance and transmitted with the data, enabling accurate write time determination at the remote system without requiring synchronous transfer or complex post-processing.
2Reliability
If SRDF/A mechanism is used to maintain write consistency and ordering for dependent writes, then data consistency is improved, but the ability to determine specific timing of individual writes deteriorates
Solution Approach 1:
The system segments the data transfer process into distinct units (chunks) and associates each chunk with a specific host write time timestamp. This segmentation allows the system to maintain write consistency through chunk-based ordering while simultaneously preserving the specific timing information for individual writes, resolving the contradiction between consistency and timing precision.
3Productivity
If data is transferred asynchronously with varying cycle times and transmission times, then transfer independence is improved, but predictability of data arrival time deteriorates
Solution Approach 1:
The system implements feedback by transmitting timestamp information from the primary storage system to the secondary storage system with each data chunk. This feedback mechanism allows the secondary system to track and determine the original host write times despite asynchronous transfer variations, eliminating the time loss and unpredictability while maintaining transfer independence.
Data Source
AI summary
Maintaining a timestamp indicating when data transferred to a remote storage system was written by a host at a local storage system includes writing a timestamp file at the local storage system, the timestamp file being part of a first chunk of data corresponding to current writes to the local storage system by the host, providing a second chunk at the local storage system, the second chunk being different from the first chunk and corresponding to writes by the host that were begun prior to beginning any of the writes for the first chunk, and transferring the writes for the second chunk to the remote storage system. Each chunk may be assigned a sequence number. The remote storage system may acknowledge receipt after receiving all data for the second chunk. The second chunk may be written to the remote storage system after receiving all data for the second chunk.