Yellow Bricks

by Duncan Epping

vSphere

Don’t know why DRS is not balancing your cluster? DRS Dump Insight!

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I was just reading up and noticed the DRS Dump Insight solution. It is a SaaS based DRS Dump Analyzer which gives you details around why your cluster is not balanced, or why certain recommendations are not made. Especially the “what if” scenarios are cool if you ask me. You can take a dump and then using the whatif feature check out what would happen to your cluster if for instance all affinity rules were dropped. Or what would happen if the DRS migration threshold is changed, or some advanced settings are used.

You can find some more info about it here, and the SaaS tool here. I hope this will make it in to the product soon in the form of a “health check”… Very useful and insightful! Oh, if you can’t access the website, try it in “Incognito Mode”. Seems there are some issues with the certificate.

vSAN 6.6.1 Performance Diagnostics Demo

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I was playing in my lab this morning and figured I would record a demo of a new feature which is part of vSAN 6.6.1. The Performance Diagnostics feature is aimed to help those running benchmarks to optimize their benchmarks, or optimize their vSAN configuration to reach their expected goals. Note that it is a “cloud connected” feature, and in order to use this you need to participate in the Customer Experience Improvement Program. This however is enabled by default in the latest releases of vSphere. This means that data is send up to the VMware cloud, anonymous, then analyzed and the results are send back to the Web Client. Anyway, enough said, just watch the demo.

Can you use the management IPs as the isolation address for HA?

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There was a question on VMTN this week about the use of the management IP’s in a “smaller” cluster as the isolation address for vSphere HA. The plan was to disable the default isolation address (default gateway) and then add every management IP as an isolation address. In this case 5 or 6 IP’s would be added. I had to think this through and went through the steps of what happens in the case of an isolation event:

  1. no traffic between secondary and primary or primary and secondary hosts (depending on whether the primary is isolated or one of the secondary hosts)
  2. if it was a secondary which is potentially isolated then the secondary will start a “primary election process”
  3. if it was the primary which is potentially isolated then the primary will try to ping the isolation addresses
  4. if it was a secondary and there’s no response to the election process then the secondary host will ping the isolation address after it has elected itself as primary host
  5. if there’s no response to any of the pings (happen in parallel) then the isolation is declared and the isolation response is triggered

Now the question is: will there be a response when the host tries to ping itself while it is isolated, as you need to add all ip-addresses to “isolation address” options for it to make sense… And that is what I tested. It will ping all isolation addresses. All but one will fail, the one that will be successful is the management IP address of the host which is isolated. (You can still ping your own IP when the NICs are disconnected even.) Leaving the VMs running as one of the isolation addresses responded.

In other words, don’t do this. The isolation address should be a reliable address outside of the ESXi host, preferably on the same network as the management.

Unbalanced Stretched vSAN Cluster

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I had this question a couple of times the past month so I figured I would write a quick post. The question that was asked is: Can I have an unbalanced stretched cluster? In other words: Can I have 6 hosts in Site A and 4 hosts in site B when using vSAN Stretched Cluster functionality? Some may refer to this as asymmetric or uneven. Either way, the number of hosts in the two locations differ.

Is this supported? In short: Yes.

The longer answer: Yes you can do this, this is fully supported but you will need to keep your selected PFTT (Primary Failures To Tolerate), SFTT (Secondary Failures To Tolerate) and FTM (Failure Tolerance Method) in to account. If PFTT=1 and SFTT=2 and FTM=Erasure Coding (RAID5/6) then the minimum number of hosts per site is 6. You could however have 10 hosts in Site A while having 6 hosts in Site B.

Some may wonder why anyone would want this, well you can imagine you are running workloads which do not need to be recovered in the case of a full site failure. If that is the case you could stick these to 1 site. (You can set PFTT=0 and SFTT=1, which would result in this scenario for that particular VM.)

That is the power of Policy Based Management and vSAN, extremely flexibility and on a per VM/VMDK basis!

VMkernel Observations (VOBs)

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I never really looked at VOBs but as this came up last week during a customer meeting I decided to look in to it a bit. I hadn’t realized there was such a large number of them in the first place. My conversation was in the context of vSAN, but there are many different VOBs. For those who don’t know VOBs are system events. These events are logged and you can create different alarms for when they are being logged.

You can check the full list of VOBs on ESXi, SSH in to it and then look at this file:

  • /usr/lib/vmware/hostd/extensions/hostdiag/locale/en/event.vmsg

When they are triggered you will see them here:

  •  /var/log/vobd.log

And as stated when you want to do something with them you can create a customer alarm. Select “specific event occuring on this object” and click next:

Now you add an event, simply click the “+” and remove the current value and simply copy/paste the VOB string in, the string will look something like this: “esx.problem.vob.vsan.pdl.offline”. Hit enter when you added it and then click “Next” and “Finish”.

I find the following useful myself:

  • esx.problem.vsan.net.redundancy.reduced
  • esx.problem.vob.vsan.lsom.componentthreshold
  • esx.problem.vob.vsan.lsom.diskerror
  • esx.problem.vob.vsan.pdl.offline
  • esx.problem.vsan.lsom.congestionthreshold
  • esx.problem.vob.vsan.dom.nospaceduringresync

There are many more, and I just listed those I found useful for vSAN, for more detail check the following links: