Idle VM's - Why should we care? (1 of 3)

The re-emergence of Virtualization technologies, such as VMware, Microsoft's Hyper-V, Xen and Linux KVM has provided organizations with the tools to create new operating system platforms ready to support the services required by the business, in minutes rather than days. 

Indeed IT itself is a service to the business.

In more recent times, Cloud computing which in itself is underpinned by Virtualization, makes use of the functionality provided to satisfy :

• on-demand resources
•           the ability to provision faster
•           rapid elasticity (refer to NIST 's description of Cloud Computing)

     Cloud computing makes full use of the underlying clustered hardware. Constant strides are being made by Virtualization vendors to improve the Virtual Machine (VM) to Host ratio, without affecting the underlying performance. 

But, you may ask "What's this got to do with Idle VMs?"

Well, as I described earlier Virtualization provides the means to easily and quickly provision virtual systems. Your CTO/CIO is going to demand a significant ROI once  an investment in both the hardware and virtualization software has been made, possibly switching the focus to an increase in the VM to Host ratio. 

“What's wrong with that?” I hear you say.  Nothing at all, as long as you keep track of what VMs you are provisioning and :

•          what resources you have granted
•          what they are for

Failure to do so will mean that your quest for a good ROI and a satisfied Chief will be in jeopardy, as you’ll encounter a term most commonly known as VM Sprawl.

More about this on Friday.

In the meantime why not register for our webinar VMware Cluster Planning'

http://www.metron-athene.com/services/webinars/capacity-management-webinars.html

Jamie Baker

Principal Consultant

5 Top Performance and Capacity Concerns for VMware - Ready Time

As I mentioned on Wednesday there are 3 states which the VM can be in:

Threads – being processed and allocated to a thread.

Ready – in a ready state where they wish to process but aren’t able to.

Idle – where they exist but don’t need to be doing anything at this time.

In the diagram below you can see that work has moved over the threads to be processed and there is some available headroom. Work that is waiting to be processed requires 2 CPU’s so is unable to fit and creates wasted space that we are unable to use at this time.

We need to remove a VM before we can put a 2 CPU VM on to a thread and remain 100% busy.

In the meantime other VM’s are coming along and we now have a 4vCPU VM accumulating Ready Time.

2 VM’s moves off but the 4vCPU VM waiting cannot move on as there are not enough vCPU’s available.

It has to wait and other work moves ahead of it to process.

Even when 3vCPU’s are available it is still unable to process and will be ‘queue jumped’ by other VM’s who require less vCPU’s.

Hopefully that is a clear illustration of why it makes sense to reduce contention by having as few vCPUs as possible in each VM.

Ready Time impacts on performance and needs to be monitored. On Monday I'll be dealing with Monitoring Memory.

Phil Bell

Consultant