We are running VCenter 2.5 server with 2 ESX 3.5 hosts. We recently aquired two additonal hosts, but before i just go throwing them into the cluster I wanted to make sure of something.
We have DRS turned on Fully Automated (at 50% aggression), this of course includes VMotion. When I add the two additional hosts, I'm assuming DRS will pick up on the additonal resources and try to move VM's around to load balance the other two hosts. So in my case, would it behoove me to change the automated DRS level to something less automated, add the two new hosts, manually load balance systems, and then turn DRS back on?
What have you folks done in the past?
Thanks in advance -
thats up to you, but we typically add hosts to an active cluster without disabling DRS. We do add our hosts into the cluster when they are in mainteance mode and then exit once the host has been added.
If your existing cluster is already providing the required resources DRS may not even move any new vm's to the newly added hosts.
What I have done when I am concerned about VM's on a DRS cluster is set the VM's that you do not want to move to manual and those can be moved via DRS you can set to fully automated. Since you can control on a per VM basis there are not big suprises when adding hosts to clusters or making changes to DRS.
I would put the hosts in the same cluster and have DRS enable so it can manage your resources effectively and dynamically so you don't have the overhead of administering those VMs resources manually. Imagine you have hundreds of VMs and wants to administer it manually would be a daunting tasks, but you can set the level of aggressiveness with DRS as mentioned. Also create a seperate anti-affinity rules so the VMs will be seperated between the hosts and never reside on the same host. Quick trick is mount devices to an .iso file so it will prevent it from VMotioning as well. Remember not to create too many rules that sometimes doesn't do what you've expected and its not recommended by VMware anyways.
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VMware vExpert 2009
iGeek Systems Inc.
VMware, Citrix, Microsoft Consultant