Hot Adding Memory to RHEV

Hi Folks,

In our last post, we took a look at the hot add CPU feature for Red Hat Enterprise Virtualization. It wasn’t a brand new feature, but still very important, especially when paired with Hot Add Memory. Which actually is a brand new feature…I have to admit, I still get excited about some of the techie stuff that I work with. We would hope so, right? That’s one of the things I really love about what I do. Go play with new toys, then show other people the new toys. Rinse, repeat. Hot add memory is a new toy for RHEV and when paired with hot add CPU, can work some real magic for just about any application that needs to be adjusted on-demand. Imagine a tier one application is under resourced, under load, and simultaneously taking resources away from other applications being hosted on the same hypervisor.

In “the old days”, this meant either migrating the problem application/virtual machine to a different hypervisor and hoping that was enough. Or migrating some or all of the other applications/virtual machines to other hypervisors and hoping that was enough. Otherwise, it meant bringing the host down and disrupting service long enough to add CPU and/or memory to the VM. Or waiting for the VM to crash, and then doing it. Regardless, this was all painful to one degree or another.

Or maybe you’re in a testing environment, or a development environment. Being able to hot add resources to a VM and not have to schedule and then wait for a reboot means more test time. More development time.

Let’s get to it. This is really an extension of the last post. Originally, I was only going to highlight the hot add memory, but my colleague Sanjay (in his infinite wisdom!!) did the demo with the hot add memory and CPU in tandem. Much better results, actually. The video shows a single instance database running virtualized in RHEV 3.6. It starts off with 108GB of RAM and 4 vCPUs. It eventually gets bumped up to  total of 16 vCPUs and 128GB of RAM. The various graphs show the utilization and transactions per minute (TPM) go from “who honestly thought this database would respond to anything in a timely fashion???” to “wow, this thing is smokin’!!”.

(Best viewed in full screen, let it ‘focus’ once you enlarge it.)

As always, feel free to comment and/or question!!

hope this helps,

Captain KVM

2 thoughts on “Hot Adding Memory to RHEV”

Agree? Disagree? Something to add to the conversation?