Virtual Disk Hierarchy Reconstruction via Content ID Matching
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Solution Overview
Problem
In computer virtualization, managing and migrating virtual disk hierarchies composed of base and delta disks is challenging due to increased data storage requirements and the need to maintain logical connections across datastores, especially when migrating virtual machines for load-balancing or decommissioning physical computers.
Innovation Solution
A method and software recreate hierarchical files on a target datastore by maintaining content identifiers for each component, allowing the child component to be writable and the parent component to be read-only, with content IDs updated upon modification, enabling efficient copying and association of delta disks with matching files on the target datastore to recreate the virtual disk hierarchy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If base and delta disks are copied together during migration to maintain logical connections, then data integrity is preserved, but data copying time and storage requirements increase significantly
Solution Approach 1:
The virtual disk hierarchy is segmented into base disk and delta disk components. During migration, only the delta disk (containing changes) is copied to the target datastore, while the base disk remains on the source datastore. This segmentation allows selective copying of only the necessary components, reducing migration time and storage requirements while maintaining data integrity through preserved hierarchical relationships.
Solution Approach 2:
A metadata structure serving as an intermediary is introduced to track and maintain the hierarchical relationships between base and delta disks across different datastores. This metadata layer enables the system to reconstruct the virtual disk hierarchy on the target datastore by referencing the source datastore, eliminating the need to copy the entire hierarchy while preserving logical connections.
2Reliability
If complete virtual disk hierarchy is migrated to ensure proper functioning, then virtual machine operation is maintained, but storage requirements and migration complexity increase
Solution Approach 1:
The virtual disk hierarchy is divided into immutable base disks and mutable delta disks. Only the delta disks containing user-specific changes are migrated to the target datastore, while base disks remain on the source datastore. This segmentation reduces the quantity of data to be migrated while ensuring virtual machine operation continuity through preserved hierarchical relationships enabled by metadata tracking.
3Adaptability or versatility
If delta disks are made writable to allow changes, then customization capability is enabled, but data integrity risks increase due to potential modifications to intermediate delta disks
Solution Approach 1:
The disk hierarchy is segmented into read-only base disks and writable delta disks. This segmentation enables customization capability by allowing writes to delta disks while protecting data integrity by keeping base disks immutable. The clear separation of responsibilities ensures that modifications are confined to appropriate layers of the hierarchy.
Solution Approach 2:
The base disk is prepared in advance as a read-only image before delta disks are created. This preliminary action establishes a stable foundation that cannot be accidentally modified, while subsequent delta disks can be safely written to. The read-only status of the base disk is established before any customization operations begin, preventing data integrity issues.
Data Source
AI summary
A method and software is described for recreating on a target datastore a set of hierarchical files that are present on a source datastore. A content identifier (ID) is maintained for each component of the set of hierarchical files. The content ID of a component is updated when its contents are modified. The child component is copied from the source datastore to the target datastore. The content ID corresponding to the parent component on the source datastore is compared with content IDs corresponding to files present on the target datastore. When a matching content ID is discovered, it infers a copy of the parent component. The matching file on the target datastore is associated with the copied child component so that the matching file becomes a new parent component to the copied child component, thereby recreating the set of hierarchical files on the target.