Virtual Disk Snapshot Consolidation via Metadata Reference Update
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Solution Overview
Problem
The performance of read IO operations in virtual disks is negatively impacted by the increased number of delta disks in a chain, leading to significant IO performance degradation during delta disk consolidation, which involves data movement operations that are resource-intensive.
Innovation Solution
A method for consolidating delta disks by modifying metadata references to point to corresponding data blocks in other delta disks, eliminating the need for data movement between delta disks, thereby reducing IO operations and maintaining performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If delta disks are consolidated by copying data from source delta disk to destination delta disk, then redundant delta disks can be removed to improve read IO performance, but data movement operations cause significant IO and CPU resource consumption and degrade IO performance during consolidation
Solution Approach 1:
Instead of copying data blocks between delta disks, the patent uses reference counting and metadata updates to logically copy the structure of delta disk references. The consolidation process creates a mapping between source and destination delta disk references without actual data movement, achieving the same structural consolidation effect with minimal resource consumption
Solution Approach 2:
The patent replaces the mechanical data copying process with a metadata-based reference system. By using reference counting and updating metadata pointers, the system achieves consolidation without physical data movement, substituting the traditional mechanical copy operation with a more efficient reference-based approach
2Reliability
If multiple snapshots of virtual disk are created to preserve historical states, then point in time copies can be maintained for backup and testing, but the number of delta disks increases forming a long chain that negatively impacts read IO performance
Solution Approach 1:
The patent merges multiple delta disk references into a consolidated structure by updating metadata pointers to point to shared data blocks. When delta disks are consolidated, their references are merged into a reduced set of active references, maintaining the ability to access historical states while reducing the chain length and improving read IO performance
Solution Approach 2:
The patent implements a universal reference system where data blocks can be referenced by multiple delta disks simultaneously. This allows a single data block to serve multiple historical states and multiple consolidation operations, reducing redundancy and improving performance across all snapshot accesses
Data Source
AI summary
A virtualized computer system employs a virtual disk. Multiple snapshots of the virtual disk can be created. After a snapshot is created, writes to the virtual disk are captured in delta disks. Two snapshots are consolidated by updating block references in snapshot meta data. Block reference update takes advantage of the fact that blocks for the two snapshot are managed within the same storage container and, therefore, can be moved in the snapshot logical space without incurring data copy operations. Consolidation of delta disks also gracefully handles failures during the consolidation operation and can be restarted anew after the system has recovered from failure.