VM Migration via Overlay Images to Reduce Downtime
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Solution Overview
Problem
VM migration from a source platform to a target platform often results in substantial downtime due to the time-consuming process of copying virtual disks, which is problematic for scenarios requiring quick mitigation such as disaster recovery or conversion between different hypervisors.
Innovation Solution
The method involves creating an overlay image of the virtual disk on an external disk, then a second overlay image on a temporary disk of the target platform, allowing a second VM to start immediately while data is written to the temporary disk, and subsequently copying both disks to a target disk, minimizing downtime through live migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If virtual disks are copied completely before starting the VM on the target platform, then data integrity is ensured, but migration downtime increases substantially
Solution Approach 1:
The patent creates an overlay image structure in advance on the target platform before the VM starts. This overlay image is configured to point to the source virtual disk, enabling the VM to immediately access and operate on the disk data without waiting for complete copying. The preliminary setup of the overlay structure resolves the contradiction by allowing data access (integrity) to begin before the copy operation finishes (time reduction).
Solution Approach 2:
The overlay image acts as an intermediary layer between the VM and the source virtual disk. Instead of directly copying the entire disk before access, the overlay image mediates by providing immediate access points to the source disk while simultaneously receiving incremental copy data. This intermediary structure enables both immediate access (reducing downtime) and progressive data transfer (ensuring integrity).
2Loss of time
If the VM is started immediately on the target platform without complete disk copying, then migration downtime is reduced, but data consistency may be compromised
Solution Approach 1:
The patent implements continuous copying of the virtual disk data in the background while the VM is running on the target platform. The copy operation does not stop when the VM starts; instead, it continues uninterrupted, progressively transferring data from source to target. This continuous action ensures that the VM has immediate access (reducing downtime) while the copying process maintains data consistency through ongoing synchronization.
Solution Approach 2:
The overlay image is preliminarily configured to redirect I/O operations to the source disk, enabling the VM to start immediately. This preliminary redirection allows the system to begin useful operations (VM execution) before the complete data transfer is finished, while the continuous copying process in the background ensures data consistency is progressively achieved without interrupting the VM's operation.
Data Source
AI summary
Disclosed is a method, comprising obtaining configuration information for a virtual machine (VM) that is to be imported from a source platform to a target platform, creating an overlay image of a virtual disk image of the VM on an external disk, creating a second overlay image of the virtual disk image on a temporary disk of the target platform, the temporary disk comprising an active layer of the virtual disk image, and the external disk comprising a backing file of the temporary disk, starting a second VM on the target platform in view of the configuration information and copying, by a processing device, the temporary disk and the external disk to a target disk on the target platform.