Virtual Machine Storage Reserve Transfer Mechanism
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Solution Overview
Problem
Existing data storage systems face challenges in maintaining data integrity when transferring virtual machines across systems, particularly due to the risk of losing exclusive access to storage devices during the transfer process, which can lead to data inconsistencies.
Innovation Solution
The introduction of a 'manage reserve command' that allows for atomic transfer of storage device reserves between host systems, using push and pull reserve commands with parameter data and Path Group Identifiers (PGIDs) to ensure exclusive access is maintained, and the implementation of a control unit to handle potential interruptions and notify systems of transfer outcomes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an unconditional command is used to transfer reserve access, then the transfer speed is improved, but data integrity is compromised because the command takes control regardless of current ownership state
Solution Approach 1:
The system applies preliminary anti-action by checking the current reserve holder state before transferring reserve access. The control unit queries whether another entity holds the device before allowing the unconditional reserve command to execute, preventing data integrity issues that would arise from conflicting reserve transfers
Solution Approach 2:
The system uses feedback by continuously monitoring the reserve holder state through queries to the control unit. The target host system receives feedback about the current ownership state before executing the reserve transfer, ensuring data integrity while maintaining transfer capability
2Reliability
If a query is performed to verify current reserve holder, then data integrity is improved, but the transfer process time increases
Solution Approach 1:
The system performs preliminary action by querying the reserve holder state in advance before initiating the reserve transfer. This ensures data integrity is verified beforehand, allowing the actual transfer command to execute quickly without repeated checks during the transfer process
3Stability of the object's composition
If exclusive access is held by a host system, then data consistency is maintained, but system adaptability decreases because other systems cannot access the device
Solution Approach 1:
The system applies dynamics by making reserve access dynamic rather than static. The control unit enables seamless transfer of reserve access between host systems through standardized commands, allowing the system to adaptively change ownership while maintaining data consistency through controlled transition mechanisms
Data Source
AI summary
A computer-implemented method for transferring a reserve to a target host, according to one embodiment, includes granting to a source system, by a control unit, a reserve for a volume of a storage device. A push reserve command is received from the source system. The push reserve command specifies: a transfer of the reserve to a target system, parameter data identifying the target system, and path information specifying the source system. The reserve is transferred only to the target system in response to release of the reserve by the source system.