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20 Cards in this Set
- Front
- Back
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Identify three admission control policies for HA: Host failures cluster tolerates
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Availability Guide, Pp 16-21
Uses a slot size mechanism. Slot sizes are logical constructs of memory and CPU and represent a single virtual machine. Slot sizes are calculated based on the largest CPU and memory reservation for a virtual machine. If no reservations are present, the default is: 32 MHz for CPU and 0MB + overhead for memory. The most restrictive between memory slots and CPU will ultimately determine the slot count You can view slot size information for the cluster using the Advanced Runtime Info hyperlink. |
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Identify three admission control policies for HA: Percentage of Cluster Resources Reserved
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Availability Guide, Pp 16-21
Implements resource constraints based upon a user-defined percentage of memory and CPU resource. Calculate failover capacity with this formula. Total Host Resources - Total Resource Requirement/Total Host Resources If you log in to vSphere and look at the Summary tab for a cluster, you can see the information related to this admission control policy in the vSphere HA pane. |
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Identify three admission control policies for HA: Specify failover hosts
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Availability Guide, Pp 16-21
The most straight-forward of the three admission control policies. Using this admission control policy will set aside whatever number of hosts you specify only for failover purposes. This host (these hosts) will never be used except in the event of an HA failover. |
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Identify heartbeat options and dependencies: Network
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Availability Guide, page 11-13
Slave nodes send a heartbeat to the master node and the master node will send a heartbeat to each of the slave nodes. The slaves do not send heartbeats to each other, but will communicate during the master node election process. Heartbeats occur every 1 second by default. Network heartbeating is dependent on the management address of the host. |
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Identify heartbeat options and dependencies: Datastore
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Availability Guide, page 14
When the master node stops receiving network heartbeats, it will use datastore heartbeats to determine if the host is network partitioned, isolated, or has completely failed. The datastore heartbeating mechanism is only used when: the master node loses connection to slave nodes, or network heartbeating fails. HA will select two datastores to use for datastore heartbeating (though this is an advanced setting you can change). These datastores must be connected to all hosts. VMFS datastores are chosen over NFS. When possible, the two datastores selected will be on different storage arrays. VMFS: Datastore heartbeating creates a file on the selected datastores for each host, and the file remains in an up-to-date state as long as the host is connected to the datastore. If the host gets disconnected from the datastore, then the file for that host will no longer be up to date. NFS: The host will write to the heartbeat file every 5 seconds. |
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Select datastores to be used for datastore heartbeating
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Availability Guide, page 14
From Inventory -> Hosts and Clusters 1. Right-click a cluster and select Edit Settings 2. Under vSphere HA, select Datastore Heartbeating 3. Choose Select only from my preferred datastores. 4. Place a checkbox next to at least two datastores you want to use for datastore heartbeating. |
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Calculate host failure requirements: Host Failures Cluster Tolerates
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Availability Guide, Pp 16-21
Calculates slot size based on largest CPU reservation and largest memory reservation - the largest of each, regardless of the VM, represents the logical object called a slot. Take all of the aggregate resources in the cluster and divide CPU by CPU slot size and memory by memory slot size. The lesser of the two numbers will give you your total slots required for failover. |
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Calculate host failure requirements: Percentage of Cluster Resources Reserved
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Availability Guide, Pp 16-21
Configure separate percentages for CPU and memory. Add all CPU used and add all memory used to get total resource required. Calculate percentage based on formula: total resources - total resources required /total resources If the percentages from this calculation are below the percentages defined, admission control will stop operations that would violate admission. |
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Calculate host failure requirements:
Specify failover hosts |
Availability Guide, Pp 16-21
Nothing to calculate, simply specify a failover host. |
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Configure advanced vSphere HA options
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Availability Guide, page 18
There are a multitude of custom HA isolation response settings that you can configure on an HA cluster. These settings are configured at the cluster level, under the vSphere HA -> Advanced Options. From Inventory -> Hosts and Clusters 1, 1. Right-click on a cluster and click Edit Settings 2. Click on vSphere HA 3. Click Advanced Options. 4. Specify an option and a value. |
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Set customized isolation response settings for virtual machines
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Availability Guide, page 30
From Inventory - > Hosts and Clusters 1. Right-click on a cluster and click Edit Settings 2. Under vSphere HA, click Virtual Machine Options. 3. Here you can set the cluster default isolation response and the isolation response for individual virtual machines. 4. Find the virtual machine you want to modify, and choose an option under the Hosts Isolation Response column. Options are: Leave powered on Power off Shut Down Use Cluster Setting (default) |
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Configure HA redundancy: Management Network
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Since HA uses the management network to send out network heartbeats, it is a good idea and best practice to make your management network redundant. There are two ways you can accomplish this:
1. Use NIC teaming on the vSS or vDS where your management network resides. 2, Add an additional VMkernel port on a separate vSS or vDS and enable it for management. |
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Configure HA redundancy: Datastore Heartbeat
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If you have a need to configure more than two heartbeats per host, you can use this advanced setting:
das.heartbeatDsPerHost Set this to the number of heartbeat datastores you want to use. If possible, ensure you have datastores that reside on two separate physical storage arrays. |
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Configure HA redundancy: Network partitions
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A network partition is created when a host, or a subset of hosts lose network communication with the master node, but can still communicate with each other. When this happens an election occurs and one of the hosts is elected as master.'
The criteria for network partition is: the hosts cannot communicate with the master node using network heartbeats, the hosts *can* communicate with the master using datastore heartbeats, the hosts are receiving election traffic. Configure HA for redundancy to avoid network partitions. |
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Configure HA related alarms and monitor an HA cluster
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Availability Guide, P 30
There are seven default alarms related to HA: 1. Insufficient vSphere HA failover resources. 2. vSphere HA failover in progress. 3. Cannot find a vSphere HA master agent. 4. vSphere HA host status. 5. vSphere HA virtual machine failover failed. 6. vSphere HA virtual machine monitoring action. 7. vSphere HA virtual machine monitoring error. There are a lot of additional alarms you can create for clusters and virtual machines related to vSphere HA. You can monitor an HA cluster using the Summary tab of any given cluster. Click the Cluster status link Click the Configuration Issues link |
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Create a custom slot size configuration
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There are two advanced settings that you can configure in order to create a custom slot size; one for CPU and one for memory.
das.slotCpuInMHz das.slotMemInMB These two advanced settings allow you to specify the maximum slot size in your cluster. If the VM has reservations that exceed the maximum slot size then the VM will use multiple slots. |
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Set custom slot size configurations
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Availability Guide, page 26
From Inventory -> Hosts and Clusters 1. Right-click a cluster and click Edit Settings. 2. Click vSphere HA. 3. Click the Advanced Options button. 4. In the option column add a new option: "das.slotMemInMB" and specify the maximum member slot size in the value column or "das.slotCpuInMHz" and specify the maximum CPU slot size in the value column. 6. Click OK when finished. |
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Understand interactions between DRS and HA
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vSphere D
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Analyze vSphere environment to determine appropriate HA admission control policy
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Dependent Upon:
Availability requirements - what resources you have available for failover and how limiting you want to be with those available resources. Cluster configuration - the size of your hosts, whether the hosts are sized the same or imbalanced Virtual Machine reservations - if you are using virtual machine reservations you need to look at the largest reservation (especially for admission control with "Host Failure Cluster Tolerates" policy) Frequency of cluster configuration changes - how often are you adding/removing hosts from your cluster. Use ost Failures Cluster Tolerates policy when you are worried about resource fragmentation (meaning there are enough resources across the hosts in the cluster, but not enough per host to meet availability requirements during failover) Use Percentage of Cluster Resources for flexibility. This is the policy recommended by VMware for most HA clusters. If you need flexibility and seamless scalability with regards to admission control, this is the policy you want to pick. Use Specify Failover Hosts when you have to have available resources above all other factors to ensure HA failover and have the budget to let a host (or hosts) stand idle. |
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Change admission control policy
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From Inventory -> Hosts and Clusters
1. Right-click on the Cluster and select Edit Settings 2. Click on vSphere HA 3. Under Admission Control Policy select one of the following: Host failures the cluster tolerates Percentage of cluster resources reserved as failover spare capacity Specify failover hosts |
