Information Technology Reference
In-Depth Information
use vMotion to move the VMs from the old servers to the newer servers, making quick work of a
server migration with no interruption of service.
Even in normal day-to-day operations, vMotion can be used when multiple VMs on the same
host are in contention for the same resource (which ultimately is causing poor performance
across all the VMs). vMotion can solve the problem by allowing an administrator to migrate any
VMs that are facing contention to another ESXi host with greater availability for the resource in
demand. For example, when two VMs are in contention with each other for CPU resources, an
administrator can eliminate the contention by using vMotion to move one of the VMs to an ESXi
host that has more available CPU resources.
vMotion moves the execution of a VM, relocating the CPU and memory footprint between
physical servers but leaving the storage untouched. Storage vMotion builds on the idea and
principle of vMotion by providing the ability to leave the CPU and memory footprint untouched
on a physical server but migrating a VM's storage while the VM is still running.
Deploying vSphere in your environment generally means that lots of shared storage—Fibre
Channel or iSCSI SAN or NFS—is needed. What happens when you need to migrate from an
older storage array to a newer storage array? What kind of downtime would be required? Or
what about a situation where you need to rebalance utilization of the array, either from a capac-
ity or performance perspective?
vSphere Storage vMotion directly addresses these situations. By providing the ability to
move the storage for a running VM between datastores, Storage vMotion enables administra-
tors to address all of these situations without downtime. This feature ensures that outgrowing
datastores or moving to a new SAN does not force an outage for the affected VMs and provides
administrators with yet another tool to increase their l exibility in responding to changing busi-
ness needs.
vSphere Distributed Resource Scheduler
vMotion is a manual operation, meaning that an administrator must initiate the vMotion opera-
tion. What if VMware vSphere could perform vMotion operations automatically? That is the
basic idea behind vSphere Distributed Resource Scheduler (DRS). If you think that vMotion
sounds exciting, your anticipation will only grow after learning about DRS. DRS, simply put,
leverages vMotion to provide automatic distribution of resource utilization across multiple ESXi
hosts that are coni gured in a cluster.
Given the prevalence of Microsoft Windows Server in today's datacenters, the use of the
term
cluster
often draws IT professionals into thoughts of Microsoft Windows Server clusters.
Windows Server clusters are often active-passive or active-active-passive clusters. However,
ESXi clusters are fundamentally different, operating in an active-active mode to aggregate and
combine resources into a shared pool. Although the underlying concept of aggregating physical
