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How VMHA works

Posted on 2014-03-30
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**If I understand when you  enable HA in a cluster. HA elects a single host as a Master.
The Master monitors the state of other hosts  and Virtual Machines and communicates with vCenter.

Q: The master uses heartbeat to detect other hosts failure or isolation, what does it use t detect VM failure?

**The Master can detect if another host is failed or isolated using Heartbeats.
 isolation is determined if the Master is still able to receive heartbeat from the datastore to which the defunct  Host is not heartbeating back to the Master

Q: I wanted to make sure that the  Datastore really does heartbeat with the Master host.

Thank you
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Question by:jskfan
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Andrew Hancock (VMware vExpert / EE MVE^2) earned 360 total points
ID: 39964874
Q: The master uses heartbeat to detect other hosts failure or isolation, what does it use t detect VM failure?

There is also a HA Agent (FDM Agent) installed on each host, which also monitors the hosts, Master, Slave, and uses VMware Tools in the VM, to detect VM failure.

You will notice, that if a VM, is protected it will state HA Protected!

Q: I wanted to make sure that the  Datastore really does heartbeat with the Master host.

It's more complicated that just heartbeats, datastore, it uses the HA Agent (FDM Agent) on each host for communications. (Master and Slaves)

If you really want to know ALL the ins and outs in great details, Duncan Epping and Frank Denneman have now written three books on VMware HA and DRS Deepdive, which I recommend to ALL VMware Admins, and should be on your bookshelf!

Duncan's website is here, and is the most comprehensive VMware HA and DRS resource and explains all the basics, give it a read, and if you need to ask further questions please post back.

see here

http://www.yellow-bricks.com/vmware-high-availability-deepdiv/

I would recommend purchasing the HA DeepDive books!
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by:Abhilash
Abhilash earned 140 total points
ID: 39964902
I second Andrew's comment. HA deepdive really gives you a clear picture of the HA concepts.
The book also comes with many live examples of what happens if a hardware failure happens etc.
Really worth buying.
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by:jskfan
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Ok…I just thought the pdf is available for everyone on Google.
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by:jskfan
ID: 39975572
Thank you Guys!
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