What is Live Migration of Virtual Machines and How Does it Work?

 Virtual Machine Live Migration

No application can afford downtime, but fortunately some downtime is completely avoidable. For those instances where you know ahead of time that system downtime is eminent such as for maintenance, moves, or natural disasters you can perform a vMotion of the workload from the server where downtime is expected to one that is not.

VMware vSphere vMotion is a zero downtime live migration of workloads from one server to another. This capability is possible across vSwitches, Clusters, and even Clouds (depending of the vSphere edition that you have). During the workload migration, the application is still running and users continue to have access to the systems they need. Talk about keeping productivity high!

Perform Live Migrations

VMware vSphere live migration allows you to move an entire running virtual machine from one physical server to another, with no downtime. The virtual machine retains its network identity and connections, ensuring a seamless migration process. Transfer the virtual machine’s active memory and precise execution state over a high-speed network, allowing the virtual machine to switch from running on the source vSphere host to the destination vSphere host. This entire process takes less than two seconds on a gigabit Ethernet network. Live migration allows you to:


  • Automatically optimize virtual machines within resource pools.
  • Perform hardware maintenance without scheduling downtime or disrupting business operations.
  • Move virtual machines away from failing or underperforming servers.

Automate and Schedule Migrations

Using VMware vSphere vMotion automated migration, you can schedule migrations at predefined times, without administrator intervention. The VMware vSphere Distributed Resource Scheduler, one of vSphere’s automated migration features, uses vMotion to optimize virtual machine performance across vSphere clusters. vMotion allows you to:


  • Migrate multiple virtual machines running any operating system across any type of hardware and storage supported by vSphere, complete with an audit trail.
  • Identify the optimal placement for a virtual machine in seconds.

Technical Details

Using the Virtual Machine File System (VMFS)

The entire state of a virtual machine is encapsulated by a set of shared storage files, such as Fibre Channel, Internet Small Computer System Interface (iSCSI) SAN or network-attached storage (NAS). VMware vSphere VMFS allows multiple installations of VMware ESX to access the same virtual machine files concurrently.

vMotion Across Boundaries and Over Long Distances

We revolutionized the concept of non-disruptive, live migration with the introduction of vMotion. With vSphere 6.0, we continue the innovation of migrating live workloads by offering new vMotion capabilities that span the boundaries of distributed switches and vCenter Servers. Furthermore, it is now possible to perform a long-distance vMotion of distances up to 100ms round-trip time (RTT). The astonishing 10x increase in supported RTT offered with Long-Distance vMotion now makes it possible for data centers physically located in New York and London to migrate live workloads between one another.

Preserving Network State

The underlying vSphere host virtualizes the networks used by the virtual machine. This ensures that even after the migration, the virtual machine network identity and network connections are preserved. A virtual machine migration with vMotion preserves the precise execution state, network identity and active network connections, so there is no downtime or disruption experienced by users.

Storage vMotion Integration

VMware vSphere 5.1 and later versions combine standard vMotion with VMware vSphere Storage vMotion in a single migration. This means you can live-migrate an entire virtual machine between hosts, between clusters or between data centers—without disruption or shared storage between the involved hosts.

Transaction Integrity

vMotion can transfer the active memory and precise execution state of the virtual machine over a high-speed network, allowing it to switch from running on the source vSphere host to the destination vSphere host. vMotion keeps the transfer period imperceptible to users by tracking ongoing memory transactions in a bitmap. Once the entire memory and system state have been copied to the target vSphere host, vMotion suspends the source virtual machine, copies the bitmap to the target vSphere host and resumes the virtual machine on the target vSphere host. Transaction integrity is ensured.

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