VMware vMotion enables the live migration of running virtual machines from one physical server to another with zero downtime, continuous service availability, and complete transaction integrity. vMotion is a key enabling technology for creating the dynamic, automated, and self-optimizing datacenter. vMotion continuously and automatically allocates virtual machines within resource pools. It also improves availability by conducting maintenance without disrupting business operations.
The advanced capability for migrating workloads without disruption is one of the features that distinguish the VxRail solution from other HCI options. In the vSphere virtual infrastructure, migration refers to moving a virtual machine from one host, datastore, or vCenter Server system to another host, datastore, or vCenter Server system. Different types of migrations exist including:
vMotion allows for live migration of virtual machines between ESXi hosts without disruption or downtime. The process is summarized in the figure below.
Figure 33. vMotion migration
With vMotion, while the entire state of the virtual machine is migrated, the data remains in the same datastore. The state information includes the current memory content and all the information that defines and identifies the virtual machine. The memory content consists of transaction data and whatever bits of the operating system and applications in memory. The definition and identification information stored in the state includes all the data that maps to the virtual machine hardware elements, including BIOS, devices, CPU, and MAC addresses for the Ethernet cards.
A vMotion migration consists of the following steps:
Enhanced vMotion Compatibility (EVC) is a cluster feature that prevents vMotion migrations from failing because of incompatible CPUs. EVC ensures that all hosts in a cluster present the same CPU feature set to virtual machines, even if the actual CPUs on the hosts differ. It prevents migration failures due to CPU incompatibility. This is on by default in VxRail systems.
Storage vMotion uses an I/O-mirroring architecture to copy disk blocks between source and destination:
The figure below illustrates the process
Figure 34. Storage vMotion
The storage-migration process copies the disk just once, and the mirror driver synchronizes the source and target blocks with no need for recursive passes. In other words, if the source block changes after it migrates, the mirror driver writes to both disks simultaneously which maintains transactional integrity. The mirroring architecture of Storage vMotion produces more predictable results, shorter migration times, and fewer I/O operations than more conventional storage-migration options. It’s fast enough to be unnoticeable to the end user. It also guarantees migration success even when using a slow destination disk.
vSphere supports the following Storage vMotion migrations: