Managing Host and Cluster Capacity

You can establish where and how many VMs you can place on a cluster or host based on the amount of CPU, memory or storage capacity available. When you add a vCenter or SCVMM managed system, Embotics® vCommander® calculates the average VM workload and the resultant capacity for each cluster. This information is updated every night as part of an automated task. You can manually update the workload and capacity information for one or more clusters or standalone hosts at any time. Whenever capacity is calculated, the information in the Capacity pane for a host or cluster is refreshed.

See also the Cluster Capacity Report.

Viewing the capacity of a host or cluster

Access through:

Views menu > Operational > Clusters > Summary tab

Views menu > Operational > Host > Summary tab

Available to:

Administrator Access Rights

To view VM capacity for a host or cluster, navigate to a host or cluster in the tree. The information is displayed in the Summary tab.

Information on the Capacity pane for a cluster or standalone host can help you determine how many VM workloads you can add, based on the available resources (CPU, memory and storage).

NotePencil-smallMemory calculations in vCommander use consumed memory.
NotePencil-smallvCommander takes VMware's HA Reserve and the Additional Reserve settings into account when performing a capacity check. See About capacity reserved for high availability failover and Setting the default reserved capacity for performance and growth below.

Any change to remaining VM capacity is indicated on the Capacity pane by arrows and values:

up_arrow indicates an increase in capacity and the number to the right of the arrow indicates what the increase in capacity is. For example, 12 up_arrow 3 means that the cluster or standalone host has the capacity for 12 VM workloads and has had an increase of three VM workloads since the last time the capacity was calculated.

down_arrow indicates a decrease in capacity and the number to the right of the arrow indicates what the decrease in capacity is. For example, 8 down_arrow 1 means that the cluster or standalone host has the capacity for 8 VM workloads and had a decrease of one VM workload since the last time the capacity was calculated.

A gray arrow right_arrow on the Capacity pane indicates that there's no change to the available capacity on a cluster or standalone host.

The following figure shows an example of the capacity available on a cluster.

Cluster-CpuStorageConstraint

Here, both CPU and storage are the constraint, and from 14 to 34 VMs can be placed on a specific host. The green arrow indicates the increase in capacity since the last update (12 using peak resources, and 34 using average resources).

The capacity available on each cluster or standalone host is calculated by vCommander using the VM workload for the cluster (shown in blue italicized text below the table). vCommander also uses the peak or average for CPU and memory usage, along with the amount of storage available on your datastores.

If one or more hosts have been excluded from the calculation of cluster capacity because they have been disconnected or because they are in maintenance mode, the Capacity pane notifies you as displayed in the example in the following figure. This figure also shows that there was no change in capacity since the previous update.

exclusion - arrows+

What's the difference between Peak and Average capacity values?

As shown in the images above, vCommander provides two capacity values: Using Peak and Using Average. vCommander monitors the usage of CPU and memory over the previous seven-day period and averages those numbers. vCommander then uses that number to calculate the average number of additional VM workloads that you could deploy on a specific host or cluster and displays that number in the "Using Average" column. During the same seven-day period, vCommander also collects information about the maximum, or peak, amount of CPU and memory used in your virtualized infrastructure. It uses that number to calculate how many additional VM workloads you could deploy in a host or cluster and displays the number in the "Using Peak" column. The number of VMs in the "Using Average" column will always be greater than or equal to the "Using Peak" column, because you can have more VMs using average resources than VMs using peak resources.

How do you decide whether to use the "Using Peak" or "Using Average" numbers? The answer depends on your requirements and the processing load that occurs in your environment. For example, if you must be careful about leaving enough capacity on your host or cluster to handle heavy processing during the week, then choose the lower number in the "Using Peak" column. By using the number in that column to guide you, you know that you will never exceed the constraints, even at your peak, for the number of VM workloads you can deploy on a host or cluster. Conversely, if your environment is such that peak usage is not of high concern (for example, in a development environment), then use the number in the "Using Average" column as a guideline to the number of additional VM workloads that you can deploy on a host or cluster.

About capacity reserved for high availability failover

vCenter allows you to reserve capacity for failover purposes. If vSphere HA and an admission control policy are set for a cluster in vCenter, vCommander takes the reserved capacity into account when calculating capacity for that cluster.

For example, if the admission control policy is configured to reserve 25% of CPU and 25% of memory on the cluster for failover purposes, vCommander will not consider that 25% as available capacity.

As another example, if the admission control policy is set to tolerate the failure of one host in a five-host cluster, and the total cluster resources are 200 GHz CPU and 1280 GB memory, vCommander uses a total CPU capacity of 160 GHz and 1024 GB (80% of the total cluster resources).

Note that while HA reserves affect how vCommander chooses the best deployment destination, they do not invalidate deployment destinations.

The following cluster properties provide information related to HA and failover:

HA Enabled

HA Failover Details

HA Failover Policy

HA Reserved CPU

HA Reserved Memory

You can add these properties to the Clusters tab in the Operational view. You can also use some of them in searches.

Manually updating capacity information for a cluster or host

Access through:

Views menu > Operational > Clusters tab

Available to:

Administrator Access Rights

To update capacity information:

1.In the Operational view, on the Clusters tab, select one or more hosts or clusters.

2.Right-click and select Update Performance and Capacity.

3.On the Confirm Update Capacity dialog, click OK.

The capacity information for the selected hosts or clusters is updated.

Setting the default VM workload

Access through:

Configuration menu > System Configuration > Capacity tab

Available to:

vCommander Role of Superuser and Enterprise Administrator

VM workload values are used to calculate the remaining capacity on hosts and clusters and to determine which resources constrain that capacity. By default, vCommander automatically calculates the average VM workload for each cluster and uses these averages in capacity calculations. However, you can set CPU, memory and storage values for a typical workload if you prefer. vCommander will then use these values in capacity calculations, rather than the average per-cluster workloads.

NotePencil-smallYou can override the default VM workload for specific clusters or standalone hosts. See Overriding the default VM workload for a specific cluster or standalone host below.

1.In the Global Capacity Defaults pane on the Capacity tab, under VM Workload, click Edit.

2.In the Global Capacity Defaults dialog, on the VM Workload tab, select one of the following:

Automatically calculate average VM workload (the default setting)

The default sample period for calculating the average workload is 7 days. Over a seven-day period, VM workloads may spike and experience non-typical values. Using a longer sample period means that these non-typical spikes have a smaller impact on the calculated average workload. To use a different sample period, enter a whole number from 1 to 180 in the Sample period (days) text field.

NotePencil-smallWith the default setting, when a new cluster is added, capacity is not calculated for the new cluster until the nightly automated task runs.

Use typical VM workload

Enter values for CPU, Memory and Storage. You can enter up to one decimal place.

3.Click OK.

Performance and capacity information for the system is updated.

Overriding the default VM workload for a specific cluster or standalone host

Access through:

Views menu > Operational > Cluster or Host

Available to:

Administrator, Operator, and Operator with Approval Access Rights

The default VM workload for all new clusters and standalone hosts is set in the Configuration menu (see Setting the default VM workload above). You can override this setting for individual clusters and standalone hosts.

NotePencil-smallThe cluster property VM Workload Overridden allows you to find clusters that are using the default capacity settings or non-default settings.

1.In the Operational view, on the Clusters tab, do one of the following:

Select a cluster, right-click and select Set Capacity Defaults.

Select a standalone host, right-click and select Set VM Workload.

cluster-cap-vm-wrkld

NotePencil-smallThe Additional Reserves tab does not appear for standalone hosts.

On the VM Workload tab, the blue text underneath Use default VM workload indicates the default setting: either "Calculated automatically with a sample period of x day(s)" or, if a typical default workload was specified, the configured values for CPU, Memory and Storage.

The values underneath Override default VM workload indicate the default workload values for this cluster: either the automatically calculated average values or, if a typical default workload was specified, the configured values for CPU, Memory and Storage.

NotePencil-smallIf you selected multiple hosts or clusters, the automatically calculated average workload values are not shown, because they are per-host and per-cluster averages.

2.If you want the VM workload to be automatically calculated for the selected clusters or hosts, no matter what the default setting is, select Automatically calculate average VM workload.

3.To set workload values for this cluster or host, select Override default VM workload and enter values for CPU, memory and storage.

When you select this option, a Calculate Average link appears.

NotePencil-smallIf you selected multiple hosts or clusters, the Calculate Average link is not displayed.

cluster-cap-vm-wrkld-calc-avg

a)Click the Calculate Average link to calculate the current VM workload values for this cluster or host.

The Calculate Average dialog appears, displaying the default sample period for calculating the average workload. Over a seven-day period, VM workloads may spike and experience non-typical values. Using a longer sample period means that these non-typical spikes have a smaller impact on the calculated average workload.

b)To use a different sample period, enter a whole number from 1 to 180 in the Sample period (days) text field, and click OK.

The values for CPU, Memory and Storage are updated. Adjust these values if desired.

5.Click OK.

If your change to the VM workload settings results in changes to the VM capacity on the cluster or host, the capacity information is refreshed (see Viewing the capacity of a host or cluster above).

Setting the default reserved capacity for performance and growth

Access through:

Configuration menu > System Configuration > Capacity tab

Available to:

vCommander Role of Superuser and Enterprise Administrator

You can reserve additional CPU and memory resources for VM growth and performance spikes. This reserved capacity is excluded from vCommander's capacity calculations, allowing you to better project when more resources are required to ensure the health of your virtualized environment. Reserved capacity is expressed as a percentage of capacity after HA reserves are removed from total capacity.

Example 1: A cluster's total capacity is 1000 GHz CPU and 1000 GB Memory. The HA reserve is set to 15%, or 150 GHz CPU and 150 GB Memory. If you set a default Additional Reserve of 25% for both CPU and memory, which translates to 212.5 GHz CPU and 212.5 GB memory for this cluster, then 637.5 GHz CPU and 637.5 GB memory are available for deployment.

Example 2: In this case, the cluster's total capacity is 1000 GHz CPU and 1000 GB memory, and HA reserve is not set. If you set a default Additional Reserve of 20% CPU and 10% memory, which translates to 200 GHz CPU and 100 GB memory for this cluster, then 800 GHz CPU and 900 GB memory are available for deployments.

NotePencil-smallYou can override the default reserved capacity for specific clusters. See Overriding the default reserved capacity for a specific cluster below.

1.In the Global Capacity Defaults pane on the Capacity tab, under VM Workload, click Edit.

2.In the Global Capacity Defaults dialog, select the Additional Reserves tab.

3.Enter values for CPU and Memory, as a percentage of cluster capacity (after HA reserved resources have been excluded). You must enter whole numbers.

Overriding the default reserved capacity for a specific cluster

Access through:

Views menu > Operational > Cluster or Host

Available to:

Administrator, Operator, and Operator with Approval Access Rights

The default reserved capacity for all new clusters and standalone hosts is set in the Configuration menu (see Setting the default reserved capacity for performance and growth above for more information and examples). You can override this setting for individual clusters and standalone hosts.

1.In the Operational view, on the Clusters tab, select a host or cluster.

2.Right-click and choose Set Capacity Defaults.

3.In the Cluster Capacity dialog, select the Additional Reserves tab.

4.Select Override default buffer.

5.Enter values for CPU and Memory, as a percentage of cluster capacity (after HA reserved resources have been excluded). You must enter whole numbers.

If your change to the capacity settings results in changes to the VM capacity on the cluster or host, the capacity information is updated (see Viewing the capacity of a host or cluster above).

Excluding new datastores from capacity calculations

Access through:

Configuration menu > System Configuration > Capacity tab

Available to:

vCommander Role of Superuser and Enterprise Administrator

By default, new datastores are included in capacity calculations. To override this behavior:

1.In the Capacity Defaults pane on the Capacity tab, click Edit.

The Datastore Configuration dialog appears.

2.To exclude new datastores from capacity calculations, disable this setting.

3.Click OK.

Specifying whether a specific datastore is included in capacity calculations

Access through:

Views menu > Operational > Cluster, Host, Folder, or Managed System

Available to:

Administrator, Operator, and Operator with Approval Access Rights

You can include or exclude a specific datastore from capacity calculations at any time. For example, you may want to exclude local storage from capacity calculations, or you may notice that a datastore was added and is not currently included in the capacity calculations performed by vCommander.

NotePencil-smallA datastore that is excluded from capacity calculations is also unavailable for automated deployment placement.

1.Select a standalone host, cluster, folder, or managed system in the tree in the Operational view.

NotePencil-small        You cannot select a host that is in a cluster.

2.Select the Datastores tab.

3.To include one or more datastores in capacity calculations, select one or more datastores from the list, right-click and select Include in Capacity.

To exclude one or more datastores from capacity calculations, select the datastores from the list, right-click and select Exclude from Capacity.

4.Click OK.