How do I migrate VMs from one hypervisor to another with minimal downtime?

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Step 1: Assess and Plan

1. Evaluate source and target hypervisors
2. Understand the features, compatibility, and limitations of each platform (e.g., VMware ESXi, Microsoft Hyper-V, KVM, Xen).
3. Identify critical workloads
4. Categorize workloads by importance and downtime tolerance to prioritize migrations.
5. Check compatibility
6. Verify VM configurations (CPU, RAM, disk types, network adapters) are supported on the target hypervisor.
7. Ensure guest operating systems and applications will function properly on the target.
8. Back up VMs
9. Perform a full backup of all VMs and their data. Test the backups to confirm they are recoverable.
10. Plan network and storage
11. Ensure the target environment has appropriate storage, networking, and compute resources.
12. Configure VLANs, IP addresses, and firewall rules as needed.

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Step 2: Prepare the Migration Tools

1. Use native migration tools where available
2. Check for vendor tools such as VMware vSphere Converter. Note: Microsoft Virtual Machine Converter (MVMC) is deprecated and no longer supported.
3. Consider third-party tools
4. Options include StarWind V2V Converter and AWS Application Migration Service (formerly CloudEndure). PlateSpin Migrate has been discontinued.
5. Export and import as fallback
6. If no tool fits, export VMs as OVF/OVA or use disk imaging (dd, qemu-img) to move raw disk files.

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Step 3: Perform a Test Migration

1. Clone a non-critical VM
2. Migrate the clone to the target hypervisor to validate the process end-to-end.
3. Verify functionality
4. Confirm the VM boots, applications start, and network configuration works on the target.

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Step 4: Execute the Migration

1. Cold migration (lower risk)
2. Shut down the VM on the source hypervisor.
3. Export the VM (OVF/OVA or disk image).
4. Import into the target hypervisor.
5. Power on and validate.
6. Live migration (minimize downtime)
7. Native live migration (vMotion, Hyper-V Live Migration) works only within the same hypervisor cluster. For cross-hypervisor moves, you need a third-party tool that replicates disks while the VM runs, then cuts over.
8. Ensure network and storage connectivity between environments before starting.
9. Convert disk formats if needed
10. Convert between formats (e.g., VMDK to VHDX, VMDK to QCOW2) using qemu-img or the converter tool of choice.
11. Reconfigure VM settings
12. Adjust hardware settings, install paravirtualized drivers (virtio, VMware Tools, Hyper-V Integration Services), and fix network interface names.

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Step 5: Post-Migration Validation

1. Verify VM functionality
2. Confirm the VM boots, applications work, and users have access.
3. Check performance
4. Monitor CPU, memory, disk, and network in the new environment. Look for contention or misconfiguration.
5. Update backup configuration
6. Add migrated VMs to backup jobs on the target platform.
7. Update documentation
8. Record new VM configurations, IP assignments, and any changes made during migration.

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Step 6: Final Cleanup

1. Decommission old VMs
2. After confirming the new VMs are stable, remove the source VMs and reclaim storage.
3. Optimize resources
4. Return freed compute and storage to the source cluster.

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Additional Tips for Minimal Downtime

• Schedule migrations during maintenance windows to reduce user impact.
• Enable HA on the target cluster before cutting over production workloads.
• Use snapshots or checkpoints on the source VM before starting, so you can roll back quickly if the migration fails. Remember: snapshots are not backups.