vMotion, Storage vMotion, DRS, Storage DRS, Storage I/O Control, VMware HA, and FT are distributed services that enable efficient and automated resource management and high availability for virtual machines.
Live migration using vMotion is the first step towards an automated and much more flexible IT environment because it truly frees the OS and application workloads from the underlying physical hardware. Virtual machines run on and consume resources from the ESXi host. vMotion enables the migration of live virtual machines from one physical server to another without service interruption. Simply saying, the notion of planned downtime goes away. This Live migration capability allows virtual machines to move from a heavily loaded server to a lightly loaded one. The result is a more efficient assignment of resources. With vMotion, resources can be dynamically reallocated across physical hosts.
Storage vMotion enables live migration of a virtual machine’s storage to a new datastore with no downtime.
Migrating single virtual machines and their disks from one datastore to another is possible because a virtual machine is composed of a set of files. Even the virtual machine’s disks are encapsulated in files. Migrating a virtual machine’s disks is accomplished by moving all the files associated with the virtual machine from one datastore to another. Extending the vMotion technology to storage helps the vSphere administrator to leverage storage tiering, perform tuning and balancing, and control capacity with no application downtime.
vSphere 5.0 uses a mirrored-mode approach for Storage vMotion. In this new architecture, Storage vMotion copies disk blocks between source and destination and replaces the need for the iterative pre-copy phase. This was used in the Changed Block Tracking (CBT) method in earlier versions of vSphere. With I/O mirroring, a single-pass copy of the disk blocks from the source to the destination is performed. I/O mirroring ensures that any newly changed blocks in the source are mirrored at the destination. There is also a block-level bitmap that identifies hot and cold blocks of the disk, or whether the data in a given block is already mirrored in the destination disk.