I have vSphere 4 standard installed on one physical server. On the server, I have about 6 Windows 2008 Servers running. One of these Windows servers is mission-critical. Is there a way to isolate this server (memory, HD access and CPU) so that regardless what other servers do, their activities would not affect the performance of this mission critical server?
You could implement reservations on the VM to ensure that it always has access to a certain amount of memory and cpu. With the hard drive access i'm not certain the best place to implement that as I don't know your storage configuration as it could be done with storage i/o control in vsphere if available or on the storage backend by utilizing a seperate lun just for that VM just to name a few possible options.
Before using reservations I would consider manipulating the shares of this vm - shares will allow you to prioritize the access of the ciritcal vms access to the those resources - shares can be set for memory, cpu and disk - but unlees you were shorted the resources on your ESX server I do not think you will have an issue since each vm runs isolated from the others -
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Yes, the host would essentially set aside that amount of physical memory just for the vm. You would likely set it for something lower than 16 if you only have 20. Possible scenario would be setting the reservation at 4GB and still manipulating the shares providing it with a greater portion of the remaining 16GB divided among the vms. The use of reservations in this case depends on how you feel about the other servers on the host, is the mission critical server most important at all costs even a degradation in performance of the other servers.
I would be sure that the guest is actually actively using that amount of RAM before setting any reservation. I would also suggest looking at adjusting shares.
1 In the vSphere Client inventory, right-click the virtual machine and select Edit Settings.
2 Click the Resources tab
This how you will be able to adjust the shares for the different resources
I would suggest that you go through the resource management guide. Better to understand than just putting in numbers. http://www.vmware.com/pdf/vsphere4/r40/vsp_40_resource_mgmt.pdf