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HA clusters testing and risks

Can I ask for  alow tech breakdown on any risks associated with vsphere HA clusters.

1) i.e. are they pretty simple to configure, is there a much an admin could configure wrongly, can you give some best practice suggestions to look for, or some bad pratice designs/configs to look for etc.

2) Also how on earth do you test this. i..e its not like you have the luxury of pulling down one of your hosts which would probably host many critical guests, so how do you test another host would save the day if one host went down? aside from purposelly pulling down the production host?

3) Do you test the HA cluster works - if so how often? What does the test involve? Do you ever encounter issues - if so what?

4) Are there any tools/scripts that will show issues with your cluster design?
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pma111
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pma111
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
1. Yes, there is lots there can go wrong, VMware HA, just requires a tick in the box, but networking setup is very important, e.g. Ensure DNS is working, IP Address are Static, Hostnames can be resolved, Default Gateways can be reached.

See also here

Troubleshooting VMware High Availability (HA) in vSphere


2. Pull power out of a host server! You test this before you go into Production! If you go into production without testing, you are a fool!

3. Regular Weekly or Monthly Checks.

4. VMware Documentation/Training Courses/Certifications.
vSphere Availability Guide
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pma111Author Commented:
3, how do accomplish 3 though - once the setup has gone live, i.e. how can you pull down a host containing business critical VM's? Do you do this out of core hours? Or how do you approach it? How long does such a test take?
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
It's easy vMotion all VMs off the host, leaving a test non-critical VM on the host to test, and then pull out the power.

We scheduled 1 hour for the test, but the test takes less than 5 mins to confirm, if working or not.
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pma111Author Commented:
Are there any technical references/terms to describe the host that a guest should be running on under normal circumstances, and the host that kicks in to restart that VM were its XYZ host to go down?
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
A VM is hosted on a Host Server, where it is originally created, unless moved by vMotion or DRS.

The VM would be restarted on any Host in the Cluster.

You can read more on this subject here

Recommended Reading
VMware vSphere 5.1 Clustering Deepdive (Volume 1)
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