Category Archives: Hyper-V

Heading Home after the 2013 MVP Global Summit

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The 2013 MVP Global Summit has come and gone already. I’m very happy to have attended and I was once again emerged in a culture of sharing knowledge and helping out our fellow MVPs and friends. Thank you Carsten!

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We shared a lot of experiences we had running Windows Server 2012 Hyper-V in production. We met up with new MVPs and veteran attendees. To all my fellow MVPs and the people at Microsoft I’d like to say that it has been an honor and a privilege to have been able to talk shop with so many highly skilled, intelligent and engaged people. What ever their background they all share a level of commitment to be all they can be in their expertise. Thank you all for taking the time and putting in the effort. I hope to see you all next time!

My Impressions on Windows Server 2012 Hyper-V Cookbook

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Having read Windows Server 2012 Hyper-V Cookbook I can safely say that if you need get up to speed with Hyper-V in Windows Server 2012 this is a great book for this purpose.

Having met Leandro Carvalho that’s not a surprise. What is pretty impressive is how he managed to get all you need to know to get going inside of one book that you can still lift with one hand. Now this is not going to make you a veteran Hyper-V enterprise architect over the weekend but it will help you get a well set up and functional Hyper-V environment running, monitored and protected. If you are already familiar with Hyper-V form previous Windows versions this book will also get you up to speed on a lot of the most important new features and improvements.

Windows Server 2012 Hyper-V Cookbook

Now a mere 305 pages are not enough to go into depth on every subject but this book will make a fine learning tool to set up a lab and take your first Windows Server 2012 Hyper-V servers / clusters into production. It also tackles some of the more intimidating stuff to some people like in place upgrades of Hyper-V clusters and disaster recovery. Details like CSV cache, Port ACL and their significance in the new Hyper-V version are not forgotten. I like that attention to detail. Knowing the vastness of what’s new in Windows Server 2012 Hyper-V I’m impressed at how well organized and effective the information is presented. So if you need to get started with Hyper-V, do it here with this book. It will make for a fine foundation to build on and move on to investigate the numerous network configurations, the VHDX format, SMB 3.0 goodness etc.

Heading Towards The 2013 Global MVP Summit

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Hello people, I’m making my way to Seattle at the moment to attend the 2013 Global MVP Summit. I’m really looking forward to this as I have a lot of feedback and questions on using Windows Server 2012 and Hyper-V in real live. That and the fact that we’ll get to discuss all this amongst each other and with the product teams. There are not many opportunities where you get to meet up with so many enthusiastic subject matter experts from all over the world.

Last month I checked my Electronic System for Travel Authorization (ESTA) papers and made sure my passport was valid.  So after packing my bag it’s now traveling time as I need to get myself to SEATAC. One of these below works just fine for that purpose I know from experience. While awaiting boarding time I’ve parked myself in LHR. If it’s anything like last year this could be considered a long-haul MVP flight Smile.

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I’m eager to meet up with friends and acquaintances again to talk shop and some fun. So Hyper-V, Cluster, Storage, Network PMs … my fellow MVPs and I are on our way. See you all very soon!

Understanding Virtual Machine Priority and Preemption Behavior

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Introduction

By reading Aidan Finn his blog You Pause A Clustered Hyper-V Host And Low Priority VMs are QUICK MIGRATED! you will learn something about how virtual machine priorities work during the pausing and draining of a clustered Hyper-V host. They are either Live or quick migrated depending on the value of the MoveTypeThreshold cluster parameter for resources of the type “Virtual Machine”. By default it’s at 2000 and that happens to be the value of the virtual machine priority “Low”.

Changing this value can alter the default behavior. For example setting the MoveTypeThreshold value to 1000 using PowerShell

Get-ClusterResourceType “Virtual Machine” | Set-ClusterParameter MoveTypeThreshold 1000

makes sure that only VMs with a priority set to “No Auto Restart”  are quick migrated. The  low priority machines would than also live migrate where by default they quick migrate.

  • Virtual Machines with Priority equal to or higher than the value specified in MoveTypeThreshold will be moved using Live Migration.
  • Virtual Machines with Priority lower than the value specified in MoveTypeThreshold will be moved using Quick Migration.

Virtual Machine Priorities
3000 = High
2000 = Medium
1000 = Low
0 = Virtual machine does not restart automatically.

Another Scenario to be aware of  to avoid surprises

Note that al this also comes into play in other scenario’s. One of them is when you attempt to start a guest that requires more resources than available on the host. Preemption kicks in and the lower priority virtual machines go into a saved state.  If you didn’t plan for this it could be a bit of a surprise, causing service interruption. What’s also important to know is that preemption kicks in even when there is no chance that putting lower priority virtual machines into saved mode will free enough resources for (all) the VMs you’re trying to start. So that service interruption might do you no good. If this is the case the Low priority VMS come back up when there are sufficient resources left.  Do note however that the ones set top “No Auto Restart” remain in a saved state. Look below for an example on how this could happen.

How does this happen?

Let’s say you have a brand new VM that has gotten 16GB of RAM as requested by the business. When that large memory guest starts it will fail due to the fact that there are not enough memory resources available on the host that only has 16GB available. But as it attempts to start, the need for memory resources is detected and preemption comes into play. The guests with “Low” and “No Auto Restart” priorities are put into a saved state as the large memory VM has the default medium priority and the MoveTypeTreshold is at the default of 2000. You need to be ware of this behavior. Preemption kicks in and the machines are still saving while starting the large memory VM has already failed as they couldn’t free enough resources anyway.

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The good new is that, as you can see below, is that the low priority guest starts again after starting the large memory guest has failed. No use keeping it saved as it can run and service customers. So the service interruption for this VM is limited but it does happen. Please also note that the guest set to No Auto Restart doesn’t come up again as it’s priority status says exactly that. So, this one becomes collateral damage.

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As you can see it’s important to know how priorities and preemption work together and behave. It also good to know that changing the threshold come into play in more situations that just pausing & draining a host of during a fail over. While the cluster will try it’s best to keep as many VMs up and running you might have some unintended consequences under certain conditions. A good understanding of this can prevent you from being bitten here. So build a small cheap lab so you can play with stuff. This helps to gain a better understanding of how features work and behave. If you want to play some more, set the priority of the memory hungry VM to high you’ll see even more interesting things happen.