Logical Volume Shadow Copy Path State Update
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Solution Overview
Problem
Existing technologies for moving logical volumes between storage appliances disrupt I/O operations and require manual rescan operations on host computers, leading to potential data unavailability and application failures due to resource imbalances.
Innovation Solution
Creating a primary copy and a shadow copy of the logical volume in a storage appliance cluster, with an initial path state setting the primary copy as active and the shadow copy as unavailable, allowing for transparent relocation without manual rescan operations by updating the path state to move host access to the shadow copy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If manual rescan operations are performed on each host computer when moving a logical volume, then the host computers can detect the new location of the logical volume, but I/O operations are disrupted and data becomes unavailable during the rescan process
Solution Approach 1:
The patent pre-registers shadow copies of the logical volume in multiple storage appliances before the actual move operation. When relocation is needed, the system simply switches the active storage appliance from the primary copy to the shadow copy, eliminating the need for post-move rescan operations on host computers. This preliminary registration of multiple possible locations allows seamless failover without disrupting I/O operations.
2Productivity
If the logical volume is moved from one storage appliance to another to balance resources, then resource utilization improves, but the movement process causes significant disruption to I/O operations
Solution Approach 1:
The patent creates shadow copies of the logical volume in multiple storage appliances simultaneously. When resource balancing is needed, the system switches to a pre-existing shadow copy rather than performing a live move operation. This copying approach allows resource redistribution without interrupting I/O operations, as the host computers continue to access the logical volume while the underlying physical location changes.
3Extent of automation
If automated logical volume relocation is implemented, then manual intervention is reduced, but the system complexity increases due to path state management
Solution Approach 1:
The patent implements dynamic path state management where storage appliances can transition between active and unavailable states. The system automatically manages these state transitions during logical volume relocation, with the multi-path I/O driver on host computers dynamically adapting to the current active storage appliance. This dynamic approach enables automated relocation while the complexity is confined to the storage appliance layer rather than requiring changes at the host computer level.
Data Source
AI summary
A primary copy and one or more shadow copies of a logical volume are created and discovered by a host rescan performed when the logical volume is initially created. Data storage resources are allocated to the primary copy, but not to the shadow copy. The initial path state of the logical volume describes the path to the primary copy as active, and the path to the shadow copy as unavailable for accessing the logical volume. Movement of the logical volume to the storage appliance providing the shadow copy can be performed without an additional host rescan, by making the shadow copy the new primary copy, making the primary copy a new shadow copy, and updating the path state of the logical volume to indicate i) that the path to the new primary copy is active, and ii) that the path to the new shadow copy is unavailable.