VMs per host and physical RAM?

[brettcw23]

I'm a little confused on the topic of host physical memory and how many guest OS's you can run based on the hosts physical memory. If I have 16GB installed on my ESX server, how much can I allocate total to my virtual machines? What does ESX use? I also understand that the more "like"guests (all windows or all UNIX) that you have, the better memory utilization. Can anyone explain that concept? Not trying to be lazy, so if there's a document I miseed, please shoot me a link! Thanks all.

[alanrenouf · Accepted solution]

The basics of it are that ESX needs a little amountof memory for the service console and then all other memory is free for your machines, the VM's will only use the amount of memory that they are actually using rather than say the 2gb that you give it.

Vmware also uses memory sharing in that common memory instructions will be shared by hosts so as you say all the common memory instructions for all windows machines will be shared, making more ram available.

Thats the very basics of it, im sure someone will add all the bells and whistles!

If you found this information useful, please consider awarding points for Correct or Helpful.

Alan Renouf

VMware, Citrix, Microsoft Consultant

UK

[mike_laspina]

Hi,

I found this article to be helpful.

[alanrenouf]

And another...

http://www.vmware.com/pdf/esx3_memory.pdf

If you found this information useful, please consider awarding points for Correct or Helpful.

Alan Renouf

VMware, Citrix, Microsoft Consultant

UK

[jayolsen]

Might want to give this a read.

[weinstein5]

alan pretty much hit on the head - the total count of vm per host is going to depend on what physical resources are consuming - typically as part of migrating from physical to virtual you measure how much memory, cpu, network and disk the machines use in the physical world - you than translate that to the resource for the vmkernel - remebering that there is transparent page sharing going on you and alan describe that will economize on memory -