5.7

Modify Usable Capacity Settings
If you activate the use of usable capacity, you can modify usable capacity settings to specify High Availability,
calculation, and buffer rules.
An administrator can modify any policy in vCenter Operations Manager at any time. The changes that the
administrator applies affect all users. Therefore, the administrator must notify the users who are working with
vCenter Operations Manager about any new settings that are applied to the policies.
The capacity buffer is a percentage of virtual machine capacity that is held in reserve to prevent the virtual
machine from consuming 100 percent of its resources.. Buffer limits apply to hosts and virtual machines. For
example, if a virtual machine is used at 50 percent capacity, adding a scenario that would simulate using
another 50 percent of capacity onto that virtual machine puts the virtual machine at its capacity limit. A peak
load might demand more performance from the virtual machine than it can deliver. The buffer limits help
prevent this event by forecasting the remaining capacity. This information appears in the following places:
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In the Time Remaining and Trend Information table on the Summary tab under the Planning tab.
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In the Total Remaining column of some views on the Views tab under the Planning tab.
NOTE For the following settings to apply, you must have set the basis for Capacity Remaining to Usable
Capacity on the Capacity and Time Remaining tab.
Prerequisites
Verify that you are logged in to a vSphere Client as an administrator, and vCenter Operations Manager is open.
Procedure
1 Click the Configuration link on the main vCenter Operations Manager page.
2 Create a new policy or open an existing policy for editing.
Option Description
To create a new policy
In the Manage Policies pane, click the Create Policy icon .
To modify an existing policy
In the Manage Policies pane, select the policy that you want to associate to
groups and click the Edit Policy icon .
3 Click 3b Usable Capacity and change the settings for usable capacity.
Option Description
Use High Availability (HA)
Configuration, and reduce capacity
If HA is configured on the clusters in your virtual environment, selecting this
option excludes the CPU and memory reserved per the HA settings when
calculating capacity scores in vCenter Operations Manager.
% of resource capacity to reserve as
buffer:
Sets the percent of reserve capacity for CPU, memory, disk I/O, disk space,
or Network I/O.
Capacity Calculation Rules
Select how to calculate capacity.
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Use last known capacity. Bases capacity calculations on the last known
capacity for the selected data interval. This setting affects the remaining
capacity. Although you expect a proportional relationship between
utilization and capacity, the average utilization might exceed the last
known capacity when the capacity drops.
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Use actual capacity. Bases capacity calculations on the average known
capacity for the selected data interval.
If you choose lUse last known capacity and your capacity has dropped over time, it is likely that your
average usage will be larger than your last known capacity. This situation can generate an alert due to
negative capacity remaining.
VMware vCenter Operations Manager Getting Started Guide
96 VMware, Inc.