Tuesday, 23 October 2012

Hot Add CPU to a Windows 2008 R2 Enterprise VM

I'm still often caught out by just how cool modern IT really is.

Today for example we had an issue with one of our businesses systems which pretty much took it out of the water.  It seems that the business had deployed a large number of additional users to this system the previous day and by now they were all starting to access the server and place significant demand on it's single vCPU.

For about an hour or more the server had been sitting there at 100% CPU (with the odd blip here and there as it churned its way through all of the work) and for new users the system was so unresponsive that it was effectively dead to them.  The few users who were already on the system and working before this CPU increase were still OK, although they were feeling the effects of the slow performance, and were still inputting data and working on their models etc.

This posed a problem.  On the one hand it was clear that this system needed to be running on more than 1 CPU now given the increased workload but on the other we didn't want to take the server out of the water (even for just a few minutes that it would take) to do this as it would mean cutting access to the users who were in and potentially causing them issues with unfinished modelling and part entered data.

Luckily enough this VM had been deployed as Windows Server 2008 R2 Enterprise.  This one decision, taken by some possibly overzealous engineer who originally built the server, saved the day as it allowed us to simple edit the VMs properties and increase the number of vCPUs allocated from 1 to 2.

Now the really cool part was watching the server via the console with task manager opened at the performance tab.  The changes were completed within vCenter and then within around 5 seconds, the OS popped up a message to state that the data was incorrect and it needed to restart task manager. Clicking OK restarted it and up popped two CPU graphs and almost instantly the CPU levels started to drop to around 55-75% utilization.
I had done this in the lab many times and new this was easily technically possible if ever we needed to do it but we had never had this occur within the few years or so that this has been possible to do. To actually use this feature in 'live' and against a running production system (of some significant importance to the business too) gave you a real sense of satisfaction.
It's great when IT just works.

Kudos to VMware and Microsoft for some pretty neat tech!

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