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vCenter 5.5 HA HeartBeat and Election Traffic

Posted on 2014-11-30
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Last Modified: 2014-12-02
Does election traffic occur over the management network or datastore connection or both?
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Question by:compdigit44
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LVL 117
ID: 40472592
By default, VMware vSphere HA comms transverses the VMkernel networks, except those marked for use with vMotion.

and if you only have one network, e.g. vMotion and Management, it will transverse this network when necessary.

However, you can use the  allowedNetworks advanced option, to change this behaviour.
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by:compdigit44
ID: 40472607
Thanks but when a HA host is network partitioned and seeing election traffic which network is it using???
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LVL 117
ID: 40472960
Datastore heartbeating is used when the cluster master no longer responds network heartbeats from the slave hosts.

A network partition is usually one where network traffic is not received over the management network.

So VMKernel Network. (except when marked vMotion)
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by:compdigit44
ID: 40473610
So not all HA members use datastore heartbeats???? You have me a bit confused now...

Sorry... ;-)
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LVL 117
ID: 40473628
Datastore heartbeating is used as an additional communication medium.

HA members use it, when necessary.

Similar to Microsoft Failover Clustering use a Private Network for heartbeat, but if the private network link goes down, they check if the other hosts is available using the Witness or Quroum disk! (same principle!).

(all this change be changed in the Advanced Settings!).
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by:compdigit44
ID: 40473761
OK but no election traffic is passed through the datastore connection correct
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LVL 117
ID: 40473772
We think of it this way, network first, datastore second.

vSphere HA uses datastore heartbeating to distinguish between hosts that have failed and hosts that reside on a network partition. Datastore heartbeating allows vSphere HA to monitor hosts when a management network partition occurs and to continue to respond to failures that occur.

Source
https://pubs.vmware.com/vsphere-51/index.jsp?topic=%2Fcom.vmware.vsphere.avail.doc%2FGUID-3E042A65-9E2A-4966-B838-0E24FA54286A.html
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by:compdigit44
ID: 40473846
Thanks I guess what threw me is since I am studying for the VCP 5.5 exam I have been reading up on HA network isolation vs network partition.

I understand that a network partition can see election traffic but if the management network is lost how is this possible or am I missing something here..

thanks again...
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Andrew Hancock (VMware vExpert / EE MVE) earned 500 total points
ID: 40473896
Depends on the definition of management network lost, if could be the default gateway is down.

I would highly recommend reading the Deep Dives on HA by By Duncan Epping and Frank Denneman.

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

Because there are also deviations when using vSAN with VMware HA which also apply....  (which are questions we've seen in the VCP! which are curve ball questions....and we feel a little crafty...).
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by:compdigit44
ID: 40474038
I have read this article but got confused but will read it again...and report back any further questions

Dude you are a Vmware Oracle!!!!
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LVL 117
ID: 40474056
Don't know about being an Oracle, but like to help, where I can.

Just watch the VMware HA, and if you have a vSAN questions!

(they are designed to trip you up!)
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by:compdigit44
ID: 40474930
I read the article again you post as see how the datastore is only used as backup basically.

On a side note, in EE how can you add post to your knowledge base?
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LVL 117
ID: 40475107
Select My Personal Knowledgebase from the Workspace icon (briefcase), and then add the URL to the question.
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