Virtual-to-Virtual (V2V) migration

V2V migration is about moving operating systems and data between virtual machines. Given the differences between hosts and virtual hardware, a virtual machine can migrate between different physical hosts, and the types of the two virtual machines need not be identical.

The need to migrate to the cloud arises in several cases:

  • when the project has exhausted the resources of the hardware platform on which it is located, and large capital investments are required for further development;
  • when the existing hardware infrastructure is not sufficiently reliable;
  • when the current cloud provider does not provide the project’s needs for the required amount of resources and their quality (for example, low network connection speeds, congested channels, high access delays to the disk subsystem, etc.).

According to this, two types of migration are distinguished – migration from hardware servers to virtual ones (Physical-to-Virtual) and migration from one cloud platform to another (Virtual-to-Virtual).

Migration to the cloud can be performed in automatic, semi-automatic, and manual modes. In each individual case, careful consideration of the technologies used on the migrated service, including the virtualization technologies used, is required.

The highest achievement in service migration is non-disruptive migration, but this can only be achieved in a limited number of cases. In the bulk, during V2V migration, there are minor service interruptions, and the task of a high-quality study of the migration procedure is to minimize the service interruption time.

There are several ways to implement a V2V migration.

V2V Offline Migration

Offline V2V migration is also known as regular migration or static migration, which requires the virtual machine to be paused before the migration.

In the shared storage scenario, only the system state will be copied to the destination host, which will be used for later recovery of the virtual machine and restoration of operation.

In the local storage scenario, the image and state of the virtual machine will be copied to the destination host at the same time.

From the user’s point of view, there is a clear period of time when the service is unavailable. This type of migration method is simple and easy to implement and is suitable for cases where service availability is not strictly required.

V2V Online Migration

An online V2V migration is also known as a live migration, which means migrating a virtual machine while the service is running normally on the virtual machine. The VM is still migrating between different physical hosts, and the logical steps are pretty much the same as offline migration.

The difference is that in order to ensure the availability of virtual machine services during the migration process, the migration process has a very short period of time. In the previous migration step, the service is running on the source host. When the migration reaches a certain stage, the destination host will have the necessary resources to start the system. After a very fast switchover, the source host will transfer the administrator role to the target host and the service will continue to run on the target host.

For the service itself, since the switchover time is very short, users will not experience service interruption, so the migration process is transparent to them. Compared to offline migration, online migration is suitable for scenarios that require high service availability.

Currently, major online migration tools such as VM converter / P2V Migrator by StarWind and XENMotion require centralized shared external storage such as SAN (storage area network) and NAS (network-attached storage) between physical machines, so when processing migration, users only need to consider running state memory migration of the operating system to get the best migration performance.

In addition, in some cases where shared storage is not used, the online storage unit migration technology can be used to implement the online migration of the V2V virtual machine. Compared to shared storage-based online migration, this type of method requires simultaneous migration of virtual machine disk images and system memory states, which degrades the overall performance of the migration. However, it manages to migrate the computing environment to a distributed local storage scenario and ensure OS services are available during the migration process, expanding the scope of online VM migration.

V2V online migration technology eliminates software and hardware recurrence and is a powerful tool for software and hardware upgrades, maintenance, and other management operations.

V2V Memory Migration Technology

For VM memory state migration, XEN and KVM adopt a basic pre-copy strategy. After the migration starts, the source host virtual machine is still running, but the target host virtual machine is disabled.

The first loop sends all the page data from the source host VM to the target host VM, and each subsequent round of the loop later sends the dirty pages that were written to the VM during the previous pre-copy round. Until the time expires when the pre-copy cycle ends, the copy completion phase will begin to be processed.

The source host will be suspended and will no longer be updated. Dirty pages in the last cycle are passed to the destination host VM. The pre-copy mechanism greatly reduces the amount of memory data that needs to be transferred during the post-copy phase, thereby significantly reducing downtime.

You can use Vincin Backup and Restore to ensure fast V2V migration without affecting the normal functioning of production systems. The virtual machine backup software supports cross-platform recovery across 10 major virtualizations, including StarWind, XenServer, oVirt, and more. It works by restoring backups of the original virtual platform to a new one without additional agents, as long as you have backups, V2V migration can be done easily.

In cross-platform recovery scenarios, both full VM recovery and instant VM recovery are applicable. You can apply for a 60-day free trial to see for yourself the ease of use and powerful functionality.