Virtualization Oversubscription - What’s so scary? Memory stats(10 of 20)

Let’s look at some stats for a single Virtual Machine

This is a 4GB VM, but it’s only accessing about 400 MB on a regular basis.  It’s got 2.6GB of memory that’s unique to itself, and 1.4GB that’s shared with other VMs.

So at least one other VM is likely to be sharing at about 1.4GB memory as well.  Given there are a lot of windows VMs in that cluster it’s likely a lot of them have similar amounts of shared memory.  If there are 10 VMs on that host then that’s about 15GB or RAM that you don’t have to have installed or rather, a few more VMs that will fit on the host.

There are also a couple of hours where the balloon driver steals some memory from the VM.  Only about 50MB and given the VMs only accessing 4 to 500MB of RAM, out of the 2.6GB that it’s using, the OS probably just released some cache to satisfy that request.

On Friday we'll be looking at Reservations and how they work.

Don't forget that registration is open for our next webinar 'Hardware's a commodity - Why bother managing capacity? http://www.metron-athene.com/services/webinars/capacity-management-webinars.html

Phil Bell

Consultant