Active-Active Storage Port Status Response Consistency
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Solution Overview
Problem
In Active-Active HA storage systems, communication failures between storage apparatuses lead to inconsistent responses to port status report requests, affecting the consistency and reliability of virtual storage apparatuses, especially in distributed data centers where path latency varies significantly.
Innovation Solution
Implementing an ALUA configuration where storage apparatuses return consistent responses to REPORT TARGET PORT GROUPS commands by designating one storage apparatus to respond with 'unavailable' or 'offline' status for ports associated with the paired apparatus, ensuring that the host computer prefers lower-latency paths and maintains system availability and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple storage apparatuses pretend to be a single virtual storage apparatus to provide a host computer, then path selection flexibility and system availability are improved, but response consistency to port status report requests deteriorates when communication failure occurs between storage apparatuses
Solution Approach 1:
Each storage apparatus independently determines its own response to port status report requests based on whether it can communicate with the paired apparatus. The storage apparatus that cannot communicate with its paired apparatus autonomously decides to return no response, while the other storage apparatus returns the status information. This self-service mechanism resolves the consistency issue without requiring complex coordination between storage apparatuses.
2Loss of information
If storage apparatuses return status information for all ports including paired apparatus ports, then complete port status information is provided, but response consistency cannot be guaranteed when communication failure occurs
Solution Approach 1:
The invention extracts the problematic port status information from the response when communication failure is detected. By omitting the status information for ports associated with the paired apparatus (which cannot be reliably obtained), the system maintains response consistency while still providing complete information when communication is successful.
3Loss of information
If the host computer requests port status information from all storage apparatuses in an HA pair, then complete path status information is obtained, but system complexity and communication overhead increase
Solution Approach 1:
The invention introduces a selective response mechanism where only the storage apparatus that can successfully communicate with the paired apparatus responds to port status report requests. This intermediary approach simplifies the communication protocol by eliminating the need for all storage apparatuses to participate in every status inquiry, reducing overall system complexity while maintaining information completeness.
Data Source
AI summary
A virtual storage apparatus based on a plurality of storage apparatuses including a first storage apparatus and a second storage apparatus is provided to a host computer. A first logical unit of the first storage apparatus and a second logical unit of the second storage apparatus are provided to the host computer in a form of a virtual logical unit. The first storage apparatus is configured to return a response to an inquiry about port statuses from the host computer designating the virtual logical unit, the response indicating that the status of the first port is a status as indicated by the first port management information and the second storage apparatus is unavailable to respond to the inquiry about port statuses. The second storage apparatus is configured to return no response to the inquiry.