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Remove Hosts from a Cluster
You can remove hosts from a cluster.
Prerequisites
Before you remove a host from a DRS cluster, consider the issues involved.
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Resource Pool Hierarchies – When you remove a host from a cluster, the host retains only the root resource
pool, even if you used a DRS cluster and decided to graft the host resource pool when you added the host
to the cluster. In that case, the hierarchy remains with the cluster. You can create a host-specific resource
pool hierarchy.
NOTE Ensure that you remove the host from the cluster by first placing it in maintenance mode. If you
instead disconnect the host before removing it from the cluster, the host retains the resource pool that
reflects the cluster hierarchy.
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Virtual Machines – A host must be in maintenance mode before you can remove it from the cluster and
for a host to enter maintenance mode all powered-on virtual machines must be migrated off that host.
When you request that a host enter maintenance mode, you are also asked whether you want to migrate
all the powered-off virtual machines on that host to other hosts in the cluster.
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Invalid Clusters – When you remove a host from a cluster, the resources available for the cluster decrease.
If the cluster has enough resources to satisfy the reservations of all virtual machines and resource pools
in the cluster, the cluster adjusts resource allocation to reflect the reduced amount of resources. If the
cluster does not have enough resources to satisfy the reservations of all resource pools, but there are
enough resources to satisfy the reservations for all virtual machines, an alarm is issued and the cluster is
marked yellow. DRS continues to run.
Procedure
1 Select the host and select Enter Maintenance Mode from the right-click menu.
2 After the host is in maintenance mode, drag it to a different inventory location, either the top-level
datacenter or a different cluster.
When you move the host, its resources are removed from the cluster. If you grafted the host’s resource
pool hierarchy onto the cluster, that hierarchy remains with the cluster.
After you move the host, you can:
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Remove the host from vCenter Server. (Select Remove from the right-click menu.)
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Run the host as a standalone host under vCenter Server. (Select Exit Maintenance Mode from the right-
click menu.)
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Move the host into another cluster.
Using Maintenance Mode
You place a host in maintenance mode when you need to service it, for example, to install more memory. A
host enters or leaves maintenance mode only as the result of a user request.
Virtual machines that are running on a host entering maintenance mode need to be migrated to another host
(either manually or automatically by DRS) or shut down. The host is in a state of Entering Maintenance Mode
until all running virtual machines are powered down or migrated to different hosts. You cannot power on
virtual machines or migrate virtual machines to a host entering maintenance mode.
Chapter 6 Using DRS Clusters to Manage Resources
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