Vmware high Availability

1- If I understand HA availability is helpful only when ESX servers are up, and one or some of them have their resources degrading in regards to the criteria set up in the cluster HA configuration.
I mean if one of ESX resources go below the threshold, VMs  get migrated to another host.
What if both ESX servers(if we only had 2) go below the threshold ?

2- In the case one ESX server unexpectedly looses power, I believe HA will not come in handy in this case. Correct ?

3-I also would like if automatic Vmotion can only be done within the Cluster?

4-in which case the VMs get restarted in another ESX server?

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Aravind SivaramanTechnical Subject Matter ExpertCommented:
Look like you are confused between HA and DRS

VMware HA - HA will restart the VM's to other host in the cluster when one of the host goes down (Host crash, Network issues, etc..)

VMware DRS - DRS analyze the cluster resoruce and place the VM on the correct host based on the resource reliability, If any the host has resource contention VM's will be vMotioned to other in the cluster

To answer you questions

2) HA will restart the VM's to other host in the cluster
3) DRS will invoke vMotion when there are resource contention and place the VM's in the cluster accordingly
4) when one of the host is not available then HA would restart the VM's

Please check http://www.yellow-bricks.com/vmware-high-availability-deepdiv/ to know more on the HA
jskfanAuthor Commented:
yes i was confused.

I forgot tha the shared storage is one of the requirement for HA as well as DRS
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
1. This is VMware DRS

2. Wrong, if a servers fails under VMware HA, ALL VMs will be restarted on another host.

3. Yes, Automatic vMotion is called VMware DRS.

See the following briefs

VMware vMotion - Migrate Virtual Machines with Zero Downtime


VMware vMotion Product Brief


VMware High Availability - Decrease Downtime and Reduce Risk


VMware High Availability (HA) Product Briefs


VMware Distributed Resource Scheduler (DRS) - Dynamic Resource Balancing


VMware Distributed Resource Scheduler (DRS) Product Briefs


Please ask questions, if you do not understand
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jskfanAuthor Commented:
So if only HA is enabled no DRS, then if one ESX host goes very low in resources, would the VMs be migrated(Vmotionned) automatically to another host, without getting rebooted in the other host.
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
No, because you do not have a license for DRS or DRS is not enabled.

You ESXi host will become oversubscribed and very slow, and affect performance of all VMs.
Aravind SivaramanTechnical Subject Matter ExpertCommented:
DRS need to be enabled for the VM's to migrate  (vMotioned) during resource contention of the host

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jskfanAuthor Commented:
Thank you Guys!
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