High Availability (HA)
VMware vSphere 4.x and above offers HA functionality. Coupled with vMotion, this ensures that if an ESX host is down, all images from that host are seamlessly moved to other nodes in the cluster and then restarted.
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VMware vSphere 4.x and above offers HA functionality. Coupled with vMotion, this ensures that if an ESX host is down, all images from that host are seamlessly moved to other nodes in the cluster and then restarted.
HA in Load/Test Environments
As with the Distributed Resource Scheduler (DRS), you should not use HA in load test or performance test environments. Enabling HA can cause significant performance impact if an ESX node goes down. In addition, HA imposes sizing restrictions on individual images. This could limit how you configure the Virtual Appliance for testing.
HA in Production Environments
Similar to DRS, HA is integral to maintaining a viable ESX cluster. CA Technologies recommends using HA in production environments, with the understanding that it could impact consistent performance of the Virtual Appliance. If an ESX node goes down, the performance of the other nodes in the cluster are also affected, because images are moved from the downed node to the surviving nodes. Either way, the Virtual Appliance is impacted:
- If it is on the downed node, performance drops as the Virtual Appliance is moved to a surviving node.
- If it is on a surviving node, performance is affected as other images are moved onto its node and resources are redistributed by the hypervisor.
Using HA dictates how much resource reservation can occur on any particular ESX host. The hypervisor does not allow memory to be reserved if the total reserved memory goes over the HA threshold required for the ESX node. If memory reservation is being used for the Virtual Appliance, this could dictate how many appliances can exist on a particular ESX node. This could also force the distribution of Virtual Appliances, trigger anti-affinity rules, or decrease the memory reservation for Virtual Appliances.