Virtual Disk Snapshot Manager Using Copy-on-Write Overlay
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Solution Overview
Problem
Existing virtual machine systems face challenges in performing 'live' management operations on virtual disks without causing downtime, as they typically require suspending virtual machine operations and inefficiently use storage resources by copying entire base images to overlay images during management operations.
Innovation Solution
Implementing a copy-on-write algorithm within a snapshot manager that creates a new overlay image for virtual disks, marking sectors as 'absent' initially, and only copying data from the base image to the overlay image during writes, allowing for 'live' management operations without interrupting virtual machine access and reducing storage resource usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the entire base image is copied to the overlay image during management operations, then a complete snapshot is created, but storage resources are inefficiently used and virtual machine operations must be suspended
Solution Approach 1:
The patent segments the base image into individual sectors and tracks them separately in the overlay image using a sector presence bitmap. Instead of copying the entire base image, only the necessary sectors are copied on-demand when written to, significantly reducing storage resource usage while maintaining snapshot consistency
Solution Approach 2:
The patent performs preliminary actions by creating an overlay image structure with sector presence tracking before actual data copying occurs. The system pre-establishes the snapshot framework and only copies data sectors when needed, avoiding the need to suspend virtual machine operations for complete image copying
2Reliability
If the entire base image is copied to the overlay image during management operations, then a complete snapshot is created, but virtual machine operations must be suspended causing downtime
Solution Approach 1:
The system performs preliminary setup by creating the overlay image structure and sector presence bitmap before any data copying. This allows the snapshot to be established without suspending virtual machine operations, maintaining productivity while ensuring snapshot consistency through on-demand sector copying
Solution Approach 2:
The patent implements a dynamic copying mechanism where sectors are copied from base image to overlay image only when they are written to during virtual machine operations. This dynamic approach allows continuous virtual machine availability while maintaining snapshot consistency, as the overlay image is updated incrementally without requiring complete image copying or VM suspension
3Quantity of substance
If sectors are copied on-demand from base image to overlay image during writes, then storage resources are saved and live operations are enabled, but the system complexity increases
Solution Approach 1:
The patent segments the image into sectors and uses a sector presence bitmap to track which sectors exist in the overlay image. This segmentation approach simplifies the complexity by providing a straightforward mechanism for on-demand sector copying and storage optimization, making the system manageable despite the enhanced functionality
Data Source
AI summary
A snapshot manager in a virtual machine monitor receives a write request comprising data from a guest operating system of a virtual machine, wherein the write request is directed to a sector of a virtual disk associated with the virtual machine. The snapshot manager writes the data from the guest operating system of the virtual machine to the sector in a base image of the virtual disk, the base image comprising a current version of the virtual disk, wherein the virtual disk comprises the base image and a overlay image, the overlay image comprising a snapshot of the base image at a previous point in time.