Virtualization Pro Tips Blog

Video Training Tiplet: Understanding DRS Groups and Rules in vCenter Server 4.1

Curious about that new DRS rule and the new host and VM groups?  I’ll show you what they mean and what they’re for in this quick Video Training Tiplet.



Hey, this is Greg Shields with another Windows IT Pro video training tiplet. Today we’re going to talk about the new DRS groups in vCenter Server version 4.1, and how the new DRS groups work with DRS rules.

If you’ve played with DRS rules before in vCenter Server you know that DRS is the function that allows vCenter to look at the performance of your various virtual machines and then rebalance those virtual machines across your available hosts. The goal is that you have the best and most optimized use of your system resources. Now if you’ve turned on DRS, you know that you can get back here to Edit Settings in your cluster and change some of the properties of DRS.

Back in the earlier versions of DRS we had the ability to create different rules that were associated with DRS. In the previous versions the rules that we had were to Keep Virtual Machines together or to Separate Virtual Machines out as they’re moving around. If you think about certain situations as virtual machines are moving around across different hosts in your environment, you may have the situation where you want a couple of virtual machines to never, ever, ever exist on the same host. Maybe they’re protected by some firewalls, and as long as they’re on different hosts you’ll know that those firewalls will be protecting their network traffic.

Consequently, you may have other situations where you want virtual machines to always reside on the same host. Maybe those virtual machines talk a lot over the network, and its better to talk over that system bus than is it to over the rest of the network in your environment. And so these rules, as DRS is moving virtual machines around, provided a mechanism for you to tell DRS when to keep virtual machines together and when to spread them apart.

In version 4.1 we now add a third rule, called Virtual Machines to Hosts, and its easiest to look at the rules first because looking at the rules will help you understand what different types of virtual machine groups and host groups that you might want to create.

Think about your environment today. You might have some virtual machines that you know must run on certain ESX hosts, or perhaps just should run on certain hosts, or must not run, or should not run on certain hosts on a group. These new virtual machines to hosts rules allow you to create a group of virtual machines and a group of hosts that behave as according to the rule that is identified here: Must run, should run, must not run, or should not run.

If you go here to DRS Groups Manager, you’ll see that we can add in virtual machines. Let’s say that we add in this Win2008-1 and we’ll call it Our VM Group. And then down here on the bottom, we’ll add a host group here, and we’ll add in the first server here and call it Our Host Group. Once we’ve completed adding these two groups in we can create a new rule called Our Rule that takes Our VM Group and Our Host Group and instructs it to behave in a certain way.

Perhaps Our VM Group must run on the hosts in that group, or just should run on the hosts in that group. This provides you some additional flexibility in how DRS goes about in doing its load balancing, but still within the constraints that you’ve created. Hopefully you’ve enjoyed this tip, and if you did, come on back to where you’ll find more great video training tiplets. Thanks for watching!


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