Datasheet

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EXPLORING VMWARE VSPHERE 5

to run. Datastores that have all the capabilities deﬁ ned in the VM storage proﬁ le are compliant

with the VM storage proﬁ le and represent possible locations where the VM could be stored.

This functionality gives vSphere administrators much greater control over the placement

of VMs on shared storage and helps ensure that the appropriate functionality for each VM is

indeed being provided by the underlying storage.

Refer to Table 1.1 to ﬁ nd out which chapter discusses proﬁ le-driven storage in more detail.

VSPHERE HIGH AVAILABILITY

In many cases, high availability (HA)—or the lack of high availability—is the key argument used

against virtualization. The most common form of this argument more or less sounds like this:

“Before virtualization, the failure of a physical server affected only one application or workload.

After virtualization, the failure of a physical server will affect many more applications or work-

loads running on that server at the same time.” We can’t put all our eggs in one basket!

VMware addresses this concern with another feature present in ESXi clusters called vSphere

HA. Once again, by nature of the naming conventions (clusters, high availability), many tra-

ditional Windows administrators will have preconceived notions about this feature. Those

notions, however, are incorrect in that vSphere HA does not function like a high-availability

conﬁ guration in Windows. The vSphere HA feature provides an automated process for restart-

ing VMs that were running on an ESXi host at a time of complete server failure. Figure 1.3

depicts the VM migration that occurs when an ESXi host that is part of an HA-enabled cluster

experiences failure.

Figure 1.3

The vSphere HA

feature will restart

any VMs that were

previously running

on an ESXi host that

experiences server

failure.

ESXi host ESXi host

VM Restart

The vSphere HA feature, unlike DRS, does not use the vMotion technology as a means of

migrating servers to another host. vMotion is applicable only for planned migrations, where

both the source and destination ESXi host are running and functioning properly. In a vSphere

HA failover situation, there is no anticipation of failure; it is not a planned outage, and therefore

there is no time to perform a vMotion operation. vSphere HA is intended to address unplanned

downtime because of the failure of a physical ESXi host.

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