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Vsphere HA

Posted on 2011-03-13
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Last Modified: 2012-06-21
Hi,

When host dies / crushes in HA enabled cluster, then VM on that host will be restarteed on other hosts in cluster.

But this will create an outage since VM needs to be restarted again.

My question is that how do we acquire VM availibility . Can we configure cluster to perform Vmotion in the event of crush

Fiyona
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Question by:toronto2456
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Expert Comment

by:coolsport00
ID: 35124288
If you have VMotion-enabled HA, your VM doesn't go down. So yes, you can. You can review the Availability Guide for more info.

Regards,
~coolsport00
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Expert Comment

by:coolsport00
ID: 35124292
Forgot to provide the Guide :)
http://www.vmware.com/pdf/vsphere4/r41/vsp_41_availability.pdf

~coolsport00
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Expert Comment

by:coolsport00
ID: 35124397
You obviously just need to meet VMotion requirements (shared storage, CPU compatibility, etc.).

~coolsport00
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Author Comment

by:toronto2456
ID: 35124450
But here is what it says in the documents you sent

 """"It protects against a server failure by restarting the virtual machines on other hosts within the cluster"""

by restarting , what it means? If the server power off and on again , then it means iVM goes down ?.



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Author Comment

by:toronto2456
ID: 35124463
or it might be that what you are mentioning is Fault Tolerant feature,,,,,is it?

Fiyona
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Author Comment

by:toronto2456
ID: 35124484
Yep, it is actually the case,

it is the blend of HA and Fault tolerant which support the continuity of the VM , not just HA.
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Expert Comment

by:coolsport00
ID: 35124565
I don't think that's entirely accurate. I will find out from VMware if a VMotion-enabled HA cluster actually brings down a VM, or regardless if it's VMotion-enabled it still restarts. If it does restart, it would be quite miniscule time-wise. If you need something to where there is absolutely *no* downtime of a VM, if it's Windows-based, you can configure it as part of a MS Cluster in addition to HA. I will (re)verify with Vmware and let you know...

~coolsport00
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Author Comment

by:toronto2456
ID: 35124606
Thanks very much,,
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Expert Comment

by:phantom024
ID: 35124619
VMware HA does not use vMotion.  vMotion is the live migration of a VM, HA simply restarts VMs from a failed host.  While a cluster can provide both vMotion and HA, they are different technologies.

If a host fails and is therefore no longer available, the running state of the VM will be lost and all that HA can do is simply register the VM on a new host and power it on.  While there is a short amount of downtime involved with this, it will be brief, and also depends on if you have customized any of the HA setting in the cluster.  However, this is still much better up time than a physical server, that in a hardware failure is down until the hardware is repaired.  

If you have a machine that simply cannot go down you should look into VMware fault tolerance, in which the VMs running state is actually placed in lockstep on two host servers.  If one fails the other will pick up the load with no downtime, and then if the resources are available will create a new running instance of the VM on an additional host so that the Fault Tolerance features are still being provided.  Be aware that there are currently some limitiations to FT enabled VMs, they cannot be vMotioned and as of now they have a 1 vcpu max.
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Author Comment

by:toronto2456
ID: 35125018
Thanks phantom024,

Very nice explanation but before closing the discussing with your thread, will you please let me know very briefly what kind of customization of the HA setting in the cluster can be made to affect the behaiiour of cluster failover to get me more familiar with the philosophy of the product

and finally ,

If Vcentre goes down, I am assuming that DRS will go down but Fault Tolerant and HA will contunuie provided that all requirements has been fulfilled.

Thanks again

Fiyona
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Accepted Solution

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phantom024 earned 500 total points
ID: 35125214
For more information on HA, I would refer you to the HA deep dive on yellow bricks, really great info here on HA, and will answer a lot of questions about how it really works better than I can try and explain in this thread.

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

You are correct in the second portion.  HA and FT will continue to function but vMotion, storage vMotion and DRS rely on vCenter.
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Author Comment

by:toronto2456
ID: 35125518
Thanks  for the information

II will check the link

F.
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Author Comment

by:toronto2456
ID: 35125521
s
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Expert Comment

by:coolsport00
ID: 35127456
Sorry for the slight delay...I know you already closed this "toronto2456", but just wanted to let you know I checked with VMware as I mentioned I would and wanted to just reconfirm what was mentioned above. Took them a little while to get back with me. I most certainly know what VMotion is and that it's "a different technology", but my interpretation of the HA Guide was that using VMotion with HA would not cause a VM restart due to the fact of how VMotion functions. I know VMotion is a vCenter feature, whereas HA is not, yet I assumed from my reading of the Guide and other resources that they both still worked together to produce a 'no downtime' scenario, but as stated above by "phantom024" (and in the Availability Guide), that is obviously not the case. Sorry for my misinterpretation of information "toronto2456", but glad you got your answer :)

Regards,
~coolsport00
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