Windows Server 2008 R2 sp1 introduced two key enhancement to Hyper-V, dynamic memory and remoteFX.  RemoteFX is a way of sharing a physical servers GPU to provide a better VDI experience and I’ll leave that for Simon to blog about, so back to dynamic memory.  This seemingly minor enhancement to Hyper-V allows you to setup minimum start up memory requirements for each VM and then increase this when they are under pressure according to rules and priorities you define (more details from a previous post of mine and its impact on SQL server ).  Of course you don’t want to be rooting around in Hyper-V in each server and setting VM to do this, you will want to manage it and so you should be in System Center Virtual Machine Manager.   To do that you’ll need the corresponding service pack (sp1) for SCVMM 2008 R2 which has been released today.

I was surprised how large it was but the download is a sliptstreamed (i.e. full ) install.  I have this short screencast on  doing the upgrade and seeing the dynamic memory showing up in  SCVMM post install..

One thing to note is that getting dynamic memory to work in the first place requires you to apply the Windows Server 2008 R2 sp1 to the physical (host) operating system.  The next step is to get the feature to be picked up in the virtual machines.If the guest operating system is Windows Server 2008 R2 or Windows 7 then applying service pack 1 to these guest operating systems will enable dynamic memory as well as providing the fixes that are included in the service pack.  For older supported operating systems such as Vista and Windows Server 2008 then reapplying the integration components to these will also turn on dynamic memory.  For more on this there is a Hyper-V Dynamic memory deployment guide on TechNet.

[added 3 April 2010]

For more on this you might want to come to our Private Cloud TechDay on 24th may in London or if you're notabloe to make that then tune into the the Managing the Private Cloud TechDays Live session on 19th April with Gordon McKenna(from Inframon) and me.