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Vmware HA

Posted on 2010-09-04
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Last Modified: 2012-05-10
when configuring High Availibility in Vmware, then one of ESX servers fails and the VMs move to another ESX server. In this case would the VMs that were on and servicing,  would move to the other ESX server as they were previously or would they reboot.??
thanks
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Question by:jskfan
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12 Comments
 
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by:coolsport00
ID: 33603979
They Vmotion to other host, meaning they're migrated while powered on.

~coolsport00
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by:coolsport00
coolsport00 earned 334 total points
ID: 33603988
So yes, they continue to run as normal.

~coolsport00
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by:jskfan
ID: 33604008
Would the DRS also reboot the VM>>
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by:coolsport00
coolsport00 earned 334 total points
ID: 33604014
No....DRS distributes resources (RAM, CPU) to VMs.
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by:jskfan
ID: 33604018
I remember we tested HA , and after we shut down one of the ESX server, the VM moved to another ESX server and rebooted.
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by:robdcoy
robdcoy earned 166 total points
ID: 33604560
Just putting my 2 cents in here, if a VM Host fails, your VM Guest would start up on another host.  The Guest system is in a "crash consistant state" meaning it would be like a power failure.  The benifets of VMware are 2 fold:

1.  The ability to move a VM Guest to another Host in order to do maintenance such as firmware updates, hardware updates, etc.

2.  The ability to quickly recover from a hardware, power, or host failure.

To avoid the "crash consistant state" you would have to implement another feature of VMware called fault tolerance.  This feature allows you to run the same machine on two hosts provided that they have common storage.

Attachment is form VMware's vCenter Server.
2010-09-04-151141.png
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Author Comment

by:jskfan
ID: 33604661
<<<Just putting my 2 cents in here, if a VM Host fails, your VM Guest would start up on another host.>>>

If I understood your statement, it means  Yes the VM machine will move to another host but it will be rebooted.  Correct?

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by:robdcoy
robdcoy earned 166 total points
ID: 33604679
Correct, but only in the event of a host failure.  You can always move them "online" using vmotion.

Also, if you are planning 2 sites, Data Center and Backup Data Center, systems will have to be shutdown and started on the secondary site or what we call, a Failover.  To do this, it requires an additional license for Site Recovery Manager or SRM.  It's not cheap but neither is building 2 Data Center so the investment is worth it.
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coolsport00 earned 334 total points
ID: 33604686
Let me further explain my statement above. If you have HA solely, yes, the VM will be "restarted" on the other host; if you have HA in your cluster as part of a *shared storage* cluster, the VM will NOT be rebooted, but VMotioned, as I mentioned above. I was going under the assumption of using HA in a shared storage/SAN environment. You can read specifically more about HA in the Availability Guide, pg. 11-12
http://www.vmware.com/pdf/vsphere4/r41/vsp_41_availability.pdf
It states in the guide that the VM does restart. In my environment, it doesn't because I have VMotioned enabled in my cluster. So, the most appropriate answer to your question is 'it depends'. It depends on how your cluster is set up. Again, if it's solely just HA, yes, the VM will reboot. Sorry I didn't further clarify.

Regards,
~coolsport00
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Author Comment

by:jskfan
ID: 33604794
in VI client console, there is a link "Migrate virtual machine" I believe this is Vmotion )kind of manual vmotion. I remember I tried this on a powered VM and moved it to another host and the VM rebooted.

When you check off  "Turn on Vmware HA"
I guess this means automatic Vmotion, in case the host fails. Correct ?

As of DRS, I guess we just need to check it off and let it do the job, because we can not see the results as long as there is no bottleneck noticed. Correct?
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by:coolsport00
coolsport00 earned 334 total points
ID: 33604810
No, migrate "can" mean VMotion, but if VMotion isn't configured (you need to configure a VMkernel Port on your vSwitch for VMotion), 'migrate' simply means a move with the VM powered off...in other words a cold migration. But, if you have VMotion configured on all ESX/i hosts in a cluster with shared storage, selecting 'migrate' yes...is VMotion. VMotion'ing to a new host does not reboot the VM. It moves the VM to another host will powered on, in whatever state the VM is in...logged onto or logged off.

I recommend keeping DRS on since it "load balances" the resources (RAM, CPU) in a cluster. It's a 'failsafe' mechanism really. So, if you go to VMotion or cold-migrate a VM to another host, but that host doesn't have the resource capacity for the extra VM, you will know as DRS will let you know. DRS doesn't cause bottlenecks...it just makes sure resources are dispersed where needed to all VMs within the cluster.

~coolsport00
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Author Comment

by:jskfan
ID: 33604819
Thanks all guys!!
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