Yellow Bricks

by Duncan Epping

VMware

Which host is selected for an HA initiated restart?

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Got asked the following question today and thought it was valuable for everyone to know the answer to this:

How is a host selected for VM placement when HA restarts VMs from a failed host?

It’s actually a really simple mechanism. HA keeps track of the unreserved capacity of each host of the cluster. When a fail-over needs to occur the hosts are ordered. The host with the highest amount of unreserved capacity being the first option. Now to make it absolutely crystal clear, HA keeps track of the unreserved capacity and it is not DRS which does this. HA works completely independent of vCenter and as we all know DRS is part of vCenter. HA also works when DRS is disabled or unlicensed!

Now one thing to note is that HA will also verify if the host is compatible with the VM or not. What this means is that HA will verify if the VMs network is available on the target host and if the datastore is available on the target hosts. If both are the case a restart will be initiated on that host. To summarize:

  1. Order available host based on unreserved capacity
  2. Check compatibility (VM Network / Datastore)
  3. Boot up!

PVSCSI and a 64bit OS

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Yesterday we had an internal discussion about the support of PVSCSI in combination with a 64bit OS. VMware’s documentation currently states the following:

Paravirtual SCSI adapters are supported on the following guest operating systems:

Windows Server 2008
Windows Server 2003
Red Hat Enterprise Linux (RHEL) 5

source

As we normally spell out every single detail this KB article is kind of ambiguous in my opinion. To clarify it, both 32bit and 64bit versions of the detailed operating systems are currently supported (vSphere 4.0). One thing to note though is that there are still limitations, for instance booting a Linux guest from a disk attached to a PVSCSI adapter is currently not supported.

vCenter Orchestrator Blog (vCO Team)

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Two of my colleagues just launched a new website. It is probably one of the few vCenter Orchestrator Blogs out there and definitely worth following.

Christophe & I (Burke) have launched a new website at http://www.vcoteam.info that we hope to use to help educate and encourage the adoption of Orchestrator for VMware automation tasks.

One of the first articles explains how to create a self provisioning portal with vCO in a detailed stepwise approach.

I am certain many more cool articles will follow. Bookmark it or add vCOTeam.info to your RSS reader.

VM Monitoring (aka VM HA) heartbeat

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I got a question around VM Monitoring (aka virtual machine level HA) this week. A customer wanted to test if VM Monitoring worked and as such disabled the NIC of the virtual machine and waited for 30 seconds for the VM Monitoring response to kick in…. nothing happened.

VM Monitoring restarts individual virtual machines when needed. VM monitoring uses a similar concept as HA, heartbeats. If heartbeats, and in this case VMware Tools heartbeats are not received for a specific amount of time the virtual machine will be rebooted. An example of when this will happen for instance is when a Windows virtual machine shows a BSOD.

The big question of course was why didn’t this trigger a response?

The answer is simple: The VMware Tools heartbeat does not use the virtual machine NIC. This heartbeat is “caught” by hostd and passed on to vCenter. vCenter uses this to show those “green/yellow/red” alarm dots. The same heartbeat is used by VM Monitoring to detect the failure of a virtual machine. Even without any NIC attached to your virtual machine these heartbeats will still be received.

One thing to keep in mind though is that when heartbeats are no longer received, by default sent out every second, VM Monitoring will check if there is any Network or Storage I/O to avoid false positives.

Question for you guys! One thing that I always wondered is how many people use VM Monitoring? And if you use it, do you use it on all VMs in every cluster?

VCAP4-DCA Exam?

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Got a couple of questions around this over the last few days and wanted to clear it up. The VCAP4-DCA (Datacenter Administrator) is 100% LAB based. For those who did the VI3 Enterprise Exam it will be similar to the second part of the exam.

In other words you will receive multiple tasks and you will get a full vSphere environment to your disposal including Service Console access, vSphere Client and vCenter. Just get the job done! It could be configuring a Distributed vSwitch or even troubleshooting and solving a problem…

In terms of preparations, make sure you have had enough LAB time. Start using the “esxcfg-” commands and make sure you know where to find what within the vSphere Client.