Yellow Cluster

[euphony]

ANyone know why a cluster in virtual centre would go yellow compared to a red cluster. Can anyone give example on why a cluster would go yellow.

I can understand a cluster going red because there are not enough resources for a configuration setting or when there is a violation on the availability constraints. Not sure why the cluster would go yellow.

[radu_dinut]

I have a yellow cluster. It says "Host x.x.x.x currently has no management network redundancy." And he is right about it :smileygrin:

[rossb2b]

Page 84 of the Resource Managment Guide describes a Yellow Cluster as:

A cluster becomes yellow when the tree of resource pools and virtual machines is

internally consistent but there is not enough capacity in the cluster to support all

resources reserved by the child resource pools. There will always be enough resources

to support all running virtual machines because, when a host becomes unavailable, all

its virtual machines become unavailable.

A cluster typically turns yellow when cluster capacity is suddenly reduced, for

example, when a host in the cluster becomes unavailable. VMware recommends that

you leave adequate additional cluster resources to avoid your cluster turning yellow.

[euphony]

If the host became unavailable should nt the cluster go red then.

[rossb2b]

From the Resoucr Managment Guide page 85:

Red Cluster

A cluster can become red because of a DRS violation or an HA violation. The behavior

of the cluster depends on the type of violation, as discussed in this section.

Red DRS Cluster

A cluster enabled for DRS becomes red when the tree is no longer internally consistent,

that is, resource constraints are not observed. The total amount of resources in the

cluster does not affect whether the cluster is red. It is possible for the cluster to be DRS

red even if enough resources are at the root level, if there is an inconsistency at a child

level.

You can resolve a red DRS cluster problem either by powering off one or more virtual

machines, moving virtual machines to parts of the tree that have sufficient resources,

or editing the resource pool settings in the red part. Adding resources typically helps

only when you are in the yellow state.

[euphony]

Do you know what it means by tree is internally consistent and is not internally consistent

[rossb2b]

A cluster will turn yellow if you have configured child resource groups with reservations that add up to your total resources and you take a host offline. Say you have 4 hosts - 3GHz each with a total of 12Ghz. You also have two child resource groups configured for 6Ghz each. If you lose a host your total resources will be reduced to 9GHz but the sum of your child resourc groups is still 12Ghz - Your cluster will turn yellow

The resource guide mentions that a cluster enabled for DRS becomes red when the tree is no longer internally consistent - meaning that resource constraints are not observed. If a user is able to start a virual machine in an unsupported way that violates the constraints, the tree is no longer consistent.

[euphony]

Have you an example when the cluster will go red. Just to see the difference between a yellow cluster.

Also regarding the yellow cluster example, would the VM's on the host failing, would they power off or would they migrate to the other hosts.

[rossb2b]

With the yellow example from above the vms are not part of the reason for the yellow cluster. Lets say you only have 2 or 3 vms running on 1 of the 4 hosts. If you shutdown one of the hosts that does not have any vms running on it, the cluster will still turn Yellow. The vms stay running and have not moved. The Cluster is yellow because the total of the child reservations cannot be met by the total available with the 3 remaining hosts.

I will post separately for the Red cluster example

[rossb2b]

Note: - If strict admission control is disabled your cluster will not turn red even it failover cannot be guaranteed.

Examples of a RED Cluster:

-If you power on enough VMs that the cluster doesn’t have enough resources to guarantee failover.

-If you have HA configured for 2 host failure in a 4 host cluster and you lose a host, your remaining 3 hosts may not be able to support a 2 host failure.

[mrubalcaba]

Here's an added reason why a cluster would go red:

A cluster can also turn red if you reconfigure a resource pool while a virtual machine is in the process of failing over. ().

I believe only a DRS cluster can become yellow. I'm probably forgetting something, but I believe that HA requirements can either be satisfied, or not. I don't think you can "over-commit" HA (which is what a yellow DRS cluster basically is).