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Table 1-1. Major Metric Concepts
Metric Description
Provisioned Amount of a resource that the user configures.
The provisioned metric might apply to the amount of
physical memory for a host or the number of vCPUs for a
virtual machine.
Usable Actual amount of a resource that the object can use.
The usable amount is less than or equal to the provisioned
amount. The difference between the provisioned amount
and usable amount stems from factors such as hardware
capacity and virtualization overhead. This overhead might
include the memory that an ESX host uses to run the host, to
support reservations for virtual machines, and to add a
buffer for high availability.
The usable metric does not apply to virtual machines.
Usage Amount of a resource that an object consumes.
The usage amount is less than or equal to the usable amount.
Demand Amount of a physical resource that the object might consume
without any existing constraints.
An object becomes constrained because of under-
provisioning or contention with other consumers of the
resource. A virtual machine might require 10GB of memory
but can only get 5GB because the virtual machine must share
resources with other virtual machines on the host.
When the demand amount is less than the usage amount, the
environment might have wasted resources. When the
demand amount is greater than the usage amount, the
environment might incur latency and exhibit decreased
performance.
Contention Effect of the difference between the amount of the resource
that the object requires and the amount of the resource that
the object gets.
This metric measures the effect of conflict for a resource
between consumers. Contention measures latency or the
amount of time it takes to gain access to a resource. This
measurement accounts for dropped packets for networking.
Limit Maximum amount that an object can obtain from a resource.
The limit sets the upper bound for CPU, memory, or disk I/O
resources that you allocate and configure in vCenter Server.
The usage amount is less than or equal to the limit amount.
The demand amount can be greater than the limit amount.
The limit amount is less than or equal to the provisioned
amount.
The default limit amount is unlimited.
Rules: Usage <= Limit
Demand can be greater than Limit .
Chapter 1 vCenter Operations Manager Features
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