Category Archive: high availability

May 31

Which isolation response should I use?

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May 31, 2012

I wrote this article about split brain scenarios for the vSphere Blog. Based on this article I received some questions around which “isolation response” to use. This is not something that can be answered by a simple “recommended practice” and applied to all scenarios out there. Note that below has got everything to do with your infrastructure. Are you using IP-Based storage? Do you have a converged network? All of these impact the decision around the isolation response.

The following table however could be used to make a decision:

Likelihood that host will retain access to VM datastores Likelihood that host will retain access to VM network Recommended Isolation policy Explanation
Likely Likely Leave Powered On VM is running fine so why power it off?
Likely Unlikely Either Leave Powered On or Shutdown Choose shutdown to allow HA to restart VMs on hosts that are not isolated and hence are likely to have access to storage
Unlikely Likely Power Off Use Power Off to avoid having two instances of the same VM on the VM network
Unlikely Unlikely Leave Powered On or Power Off Leave Powered on if the VM can recover from the network/datastore outage if it is not restarted because of the isolation, and Power Off if it likely can’t.

“Which isolation response should I use?” originally appeared on Yellow-Bricks.com. Follow us on Twitter and Facebook.
Available now: vSphere 5 Clustering Deepdive. (paper | e-book)

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Permanent link to this article: http://www.startswithv.com/2012/05/31/which-isolation-response-should-i-use/

May 25

How do I use das.isolationaddress[x]?

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May 25, 2012

Recently I received a question on twitter how the vSphere HA advanced option “das.isolationaddress” should be used. This setting is used when there is the desire or a requirement to specify an additional isolation address. The isolation address is used by a host which “believes” it is isolated. In other words, if a host isn’t receiving heartbeats anymore it pings the isolation address to validate if it still has network access or not. If it does still have network access (response from isolation address) then no action is taken, if the isolation address does not respond then the “isolation response” is triggered.

Out of the box the “default gateway” is used as an isolation address. In most cases it is recommended to specify at least one extra isolation address. This would be done as follows:

  • Right click your vSphere Cluster and select “Edit settings”
  • Go to the vSphere HA section and click “Advanced options”
  • Add “das.isolationaddress0″ under the option column
  • And add the “IP Address” of the device you want to use as an isolation address under the value column

Now if you want to specify another isolation address you should add “das.isolationaddress1″. In total 10 isolation addresses will be used. Keep in mind that all of these will be pinged in parallel! Many seem to be under the impression that this happens sequential, but that is not the case!

Now if for whatever reason the default gateway should not be used you could disable this by adding the “das.usedefaultisolationaddress” to “false”. A usecase for this would be when the default gateway is a “non-pingable” device, in most scenarios it is not needed though to use “das.usedefaultisolationaddress”.

I hope this helps when implementing your cluster,

“How do I use das.isolationaddress[x]?” originally appeared on Yellow-Bricks.com. Follow us on Twitter and Facebook.
Available now: vSphere 5 Clustering Deepdive. (paper | e-book)

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Permanent link to this article: http://www.startswithv.com/2012/05/25/how-do-i-use-das-isolationaddressx/

Apr 30

With vSphere 5.0 and HA can I share datastores across clusters?

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April 30, 2012

I have had this question multiple times by now so I figured I would write a short blog post about it. The question is if you can share datastores across clusters with vSphere 5.0 and HA enabled. This question comes from the fact that HA has a new feature called “datastore heartbeating” and uses the datastore as a communication mechanism.

The answer is short and sweet: Yes.

For each cluster a folder is created. The folder structure is as follows:

/<root of datastore>/.vSphere-HA/<cluster-specific-directory>/

 

The “cluster specific directory” is based on the uuid of the vCenter Server, the MoID of the cluster, a random 8 char string and the name of the host running vCenter Server. So even if you use dozens of vCenter Servers there is no need to worry.

Each folder contains the files HA needs/uses as shown in the screenshot below. So no need to worry around sharing of datastores across clusters. Frank also wrote an article about this from a Storage DRS perspective. Make sure you read it!

PS: all these details can be found in our Clustering Deepdive book… find it on Amazon.

“With vSphere 5.0 and HA can I share datastores across clusters?” originally appeared on Yellow-Bricks.com. Follow us on Twitter and Facebook.
Available now: vSphere 5 Clustering Deepdive. (paper | e-book)

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Permanent link to this article: http://www.startswithv.com/2012/04/30/with-vsphere-5-0-and-ha-can-i-share-datastores-across-clusters/

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