Host-Based Data Migration Reservation Handling
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Solution Overview
Problem
Host-based data migration in clusters is challenging due to concurrent access by other hosts, leading to loss of control over source and target LUNs, resulting in unpredictable divergence and potential application failures, as conventional methods inadequately handle reservations during data migration.
Innovation Solution
An improved data migration technique that dynamically handles control I/Os based on the migration state and the type of operation (query or setting) for reservations and logical information, ensuring that reservation information is properly transferred from the source to the target LUN, maintaining exclusive access and preventing data corruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If reservations are treated as ordinary control I/O requests during data migration, then the migration tool can process them through standard I/O paths, but this causes reservations to not be properly transferred from source LUN to target LUN, leaving LUNs vulnerable to corruption
Solution Approach 1:
The patent segments control I/O requests into two distinct categories: data I/O requests and control I/O requests. By creating separate processing paths for these two types of requests, the system ensures that reservations (control I/O) are handled differently from regular data operations. This segmentation allows the migration tool to properly transfer reservation information from source to target LUN while still processing data I/O through standard paths.
Solution Approach 2:
The patent introduces an intermediary mechanism in the form of a migration tool that intercepts control I/O requests between the host and storage system. This intermediary captures reservation commands, processes them through special handling logic, and ensures they are properly applied to both source and target LUNs during migration. The intermediary prevents control I/O from being lost or misrouted while maintaining transparency for applications.
2Device complexity
If the migration tool directs all control I/O requests to the current selected LUN (source or target), then processing is simplified, but this causes the selected LUN to be left in an unreserved state, making it vulnerable to writes by other hosts
Solution Approach 1:
The patent applies preliminary action by ensuring that reservation commands are processed and applied to both source and target LUNs before the migration tool switches between them. By pre-establishing reservations on both LUNs during the migration process, the system prevents the selected LUN from being left in an unreserved state. This proactive approach ensures continuous protection against unauthorized writes throughout the migration states.
3Productivity
If data migration is conducted in a cluster environment with multiple hosts accessing the same LUNs, then resource utilization is improved, but other hosts can cause the migration host to lose control of LUN contents, causing unpredictable divergence
Solution Approach 1:
The patent applies preliminary anti-action by using reservations to preemptively block other hosts from accessing or modifying the source and target LUNs during the data migration process. By establishing exclusive access rights before migration operations occur, the system prevents other cluster hosts from causing content divergence or corruption. This protective measure allows the migration host to maintain control while the cluster continues to utilize other resources.
Data Source
AI summary
An improved technique migrating data from a source LUN (logical unit) to a target LUN manages control I/O's in a manner that depends on the current state of data migration and on whether the control I/O's specify that reservation information for a LUN is to be set or queried. Control I/O's specifying reservation settings during the different states of migration are treated the same way as data WRITEs during those respective states, and control I/O's specifying reservation queries during different migration states are treated the same way as data READs during those respective states.