Term
| Define VM-VM Affinity/Anti Affinity Rules |
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Definition
specifies whether VMs should run on the same host or be kept on separate hosts.
Might want to keep VMs on the same host for performance reasons
Might want to keep VMs separated to ensure certain VMs remaining running if one host fails.
If to VM-VM rules conflict with each other, the older rule will take precedence over the newer one and the newer one will be disabled.
DRS will also give higher precedence to preventing violation of ant-affinity rules than that of affinity.
Source: blog.mwpreston.net |
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Term
| What happens if two VM-VM rules conflict? |
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Definition
| The older rule takes precedence and the newer rule is disabled |
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Term
| Define VM-Host Affinity/Anti-Affintiy Rules |
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Definition
Specifies whether or not VMs in a VM DRS group should or shouldn't run on hosts in a host DRS group.
May want to keep certain VMs running on certain hosts due to licensing issues.
Options to specify whether the rule is a hard rule (must not/must run on hosts) or a soft rule (should/should not run on hosts).
Source: blog.mwpreston.net |
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Term
| What is a soft rule and a hard rule with VM-Host anti-affinity rules/affinity rules |
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Definition
Soft role: VM should/should not run on a given host
Hard rule: VM must/must not run on a given host |
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Term
| Which takes higher precedence: preventing violation of anti-affinity rules or affinity rules? |
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Definition
| Anti-affinity rules take precedence |
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Term
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Definition
| Host monitoring is one of the features used by HA to determine whether a host is isolated. It works by ESXi hosts within the cluster sending heartbeats over the network between each other. |
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Term
| How do you enable/disable host monitoring? |
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Definition
| In vSphere client, under host and clusters view, right click DRS/HA cluster and edit settings. Click on vSphere HAS and select or deselect 'Enable Host Monitoring' |
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Term
| Define Virtual machine monitoring |
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Definition
| Acts much like HA, however it will restart individual virtual machines if their VMware tools heartbeats are not received within a set time. |
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Term
| Where is Virtual Machine Monitoring enabled/disabled |
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Definition
| In the VM Monitoring section of the HA configuration options on the cluster |
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Term
| How is monitoring sensitivity configure for Virtual machine monitoring? |
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Definition
Monitoring sensitivity is configurable as follows
Low – VM will restart if no heartbeat between host and VM within 2 minutes. VM will restart 3 times every 7 days.
Medium – no heartbeat for 60 seconds, 3 restarts within 24 hrs.
High – no heartbeat for 30 seconds, 3 restarts per hour.
Custom – allows you to customize interval, number of restarts and time frame.
These sensitivities are the same options for application monitoring. |
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Term
| Define Application Monitoring |
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Definition
Restarts individual VMs if their VMware tools application heartbeats are not received within a set time.
Enabled/Disabled within the VM Monitoring section of the HA configuration options on the cluster
In order to use application monitoring, you must obtain the appropriate SDK or use an application that supports VMware application monitoring and set it up to send heartbeats.
Deployed on a per VM basis. I believe it uses the same monitoring sensibility as VM Monitoring. |
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Term
| What levels can VM monitoring be set on |
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Definition
| Global cluster setting as well as VM level setting |
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Term
| What levels can Application Monitoring be set on? |
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Definition
| Enabled in the VM Monitoring section of the HA configuration options on the cluster. Deployed on a per VM basis |
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Term
| What is the function of Admission control in HA? |
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Definition
| Admission control ensures that sufficient resources are available in a cluster to provide failover protection and ensure that VMs get their reservations. |
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Term
| Without admission control, what are the minimum requirements for vSphere HA |
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Definition
| vSphere will ensure that at least two hosts are powered on in a cluster and that all VMs are able to be consolidated on to a single host |
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Term
| What restrictions could Admission control apply in order to ensure that sufficient resources are available in a cluster to provide failover protection? |
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Definition
| Prevent you from powering on a VM, migrating a VM into a cluster, increasing the amount of resources on a VM |
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Term
| Name the 3 types of admission control policies you can use with HA |
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Definition
1. Host Failures Cluster Tolerates
2. Percentage of Cluster Resources Reserved
3. Specify Failover hosts |
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Term
| Define the 'Host Failures Cluster Tolerates' Admission Control policy |
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Definition
* Specify the number of hosts that a cluster can tolerate if there failure on
* vSphere will reserve the required resources to restart all the VMs on those failed hosts |
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Term
| Define the 'Percentage of Cluster Resources Reserved' Admission Control policy |
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Definition
| * HA will reserve a specific percentage of cluster CPU and memory for recovery host failures |
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Term
| Define the 'Specify Failover Hosts' Admission Control policy |
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Definition
* Specify the hosts you want to use for failover
* This host will then not be available to run VMs, it's set aside 100% for HA |
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Term
| What considerations should you be aware of when determining your failover methodology? |
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Definition
Resource Fragmentation
When there are enough resources available, but they are located on multiple hosts, thus one host doesn’t have enough resources to run the VM.
The host failures cluster tolerates avoids this by using it's slot mechanism.
The percentage policy does not since it's looking at a percentage of resources based on the cluster itself.
Flexibility of Failover Resource Reservation
Host Failures allows you specify number of hosts that can fail
Percentage allows you to look at the cluster resources as a whole
Failover hosts allows you to determine where and which hosts will be used.
Heterogeneity of Cluster
When using large virtual machines, the Host Failures cluster tolerates slot size will be impacted and grow very large, thus giving you unexpected results, especially if you use reservations.
The remaining two policies are not so much affected by the 'monster VM'
Source: blog.mwpreston.net |
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