Virtual Computer Live Migration via Dummy FC-HBA
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Solution Overview
Problem
In virtual computer systems employing the I/O pass-through mode, live migration of logical partitions (LPARs) is hindered by the need for OS login and logout times that can exceed 30 seconds, causing temporary disk access disruptions and incompatibility with FC path switching due to unique WWN constraints and lack of FC path switching modules in x86 architecture OSs.
Innovation Solution
A method involving a hypervisor that creates logical HBAs and manages address conversions to switch I/O paths during live migration, using a dummy WWN for seamless FC path switching, allowing continuous OS access to memory devices without recognizing the path change to the OS.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If OS login/logout processing is performed during LPAR migration, then the OS can access the same LU on the destination computer, but the migration time exceeds 30 seconds causing service interruption
Solution Approach 1:
The patent applies preliminary action by pre-establishing the FC path from the source LPAR to the destination computer's physical HBA before migration. A dummy logical HBA is created on the source computer and connected to the destination's physical HBA in advance, allowing the OS to maintain disk access without login/logout processing during migration.
Solution Approach 2:
The patent uses a dummy logical HBA as an intermediary component. This dummy logical HBA is created on the source computer, assigned a dummy WWN, and connected to the destination physical HBA. It serves as a mediator that allows the OS to access storage through a different physical path without requiring re-login, thus enabling live migration.
2Reliability
If unique WWN constraints are enforced for SAN security, then data security is protected, but FC path switching becomes incompatible with live migration
Solution Approach 1:
The patent segments the WWN identification function by introducing a dummy logical HBA with a dummy WWN that is separate from the source LPAR's actual WWN. This segmentation allows the system to maintain unique WWN constraints for security while creating a separate identification path for migration purposes.
Solution Approach 2:
The patent changes the WWN parameter by assigning a dummy WWN to the dummy logical HBA instead of using the source LPAR's original WWN. This parameter change enables the destination computer to accept the connection without WWN conflict, while the OS remains unaware of the WWN change due to the transparent path switching.
3Device complexity
If x86 architecture OSs are used without FC path switching modules, then system simplicity is maintained, but live migration with FC path switching cannot be achieved
Solution Approach 1:
The dummy logical HBA acts as an intermediary that handles the FC path switching functionality externally, eliminating the need for FC path switching modules within the x86 OS itself. The path switching is performed at the hypervisor level through the dummy logical HBA, keeping the OS simple while enabling live migration.
Solution Approach 2:
The patent replaces the need for FC path switching modules in the OS with a hypervisor-level mechanism. Instead of implementing complex FC path switching logic in the x86 OS, the functionality is substituted by the dummy logical HBA and address conversion table in the hypervisor, maintaining OS simplicity while achieving live migration.
Data Source
AI summary
A live migration in a virtual computer system. On a source physical computer, the control information area of the source logical FC-HBA (managed by an OS) is copied to the control information area of a dummy logical FC-HBA managed by a hypervisor. After an FC login to the dummy FC-HBA, an address conversion table is rewritten so that a host physical address for referring to the control information area of a logical HBA1′ can be referred to using a guest logical address for referring to the control information area of the source FC-HBA. After the FC logout of the source FC-HBA, using a WWN of the FC used for the FC logout, a login to the destination logic FC-HBA is performed. Next, the OS on the source computer is taken over by the destination computer. Therefore, the disk accessed on the source computer can be accessed from the destination FC-HBA.