Idle VMs - Why should we care? (3 of 3)

At the end of last week I looked at the impact idle VM’s can have on CPU utilization and memory overhead today I’m going to look at the amount of Disk or Datastore space usage per Idle VM. 

Each one will have associated VMDK (disk) files.  The files are stored within a Datastore, which in most cases is hosted SAN or NAS storage and shared between the cluster host members.  If VMDKs are provisioned as "Thick Disks" then the provisioned space is locked out within the Datastore for those disks.

To illustrate this an example of a least worst case scenario would be:  100 Windows  idle VMs have been identified across the Virtual Infrastructure and each VM has a "Thick" single VMDK of 20GB used to house the operating system.  This would then equate to 2TB of Datastore space being locked for use by VMs that are idle.  You can expand this further by, making an assumption  that some if not all VMs are likely to have more disks and of differing sizes.

The simple math will show you how much Datastore space is being wasted.

There is a counter to this, known as Thin Provisioning.  By using Thin disks, in which the provisioned disk size is reserved but not locked you  would not waste the same amount of space as you would by using Thick Disks.  Using Thin Provisioning also has the added benefit of being able to over allocate disk space thus leading to a reduction in the amount of up front storage capacity required, but only incurring minimal overhead.

Idle VMs -  why you should care.

Identifying Idle VMs, questioning whether they are required, finding out who owns them and  removing them completely will reduce or help eliminate VM sprawl and help to improve the performance and capacity of the Virtual Infrastructure by:

·       reducing unnecessary timer interrupts

·       reducing allocated vCPUs

·       reducing unnecessary CPU and Memory overhead

·       reduce used Datastore space

·       lead to more efficient use of your Virtual Infrastructure, including improved VM to Host ratios and reduction in additional hardware.

Don't forget to sign up for our VMware vSphere Capacity and Performance Essentials online workshop commencing on Dec 6th.

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

Jamie Baker

Principal Consultant

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

Idle VMs - Why should we care? (2 of 3)

In my previous blog I mentioned the term VM Sprawl and this is where Idle VMs are likely to factor. 

Often VMs are provisioned to support short term projects,  for development/test processes or for applications which have now been decommissioned.  Now idle, they’re left alone, not bothering anyone and therefore not on the Capacity and Performance teams radar.

Which brings us back to the question.  Idle VMs - Why should we care? 

We should care, for a number of reasons but let's start with the impact on CPU utilization.

When VMs are powered on and running, timer interrupts have to be delivered from the host CPU to the VM.  The total number of timer interrupts being delivered depends on the following factors:

·       VMs running symmetric multiprocessing (SMP), hardware abstraction layers (HALs)/kernels require more timer interrupts than those running Uniprocessor HALs/Kernels.

·       How many virtual CPUs (vCPUs) the VM has.

Delivering many virtual timer interrupts can negatively impact on the performance of the VM and can also increase host CPU consumption.  This can be mitigated however, by reducing the number of vCPUs which reduces the timer interrupts and also the amount of co-scheduling overhead (check CPU Ready Time). 

Then there's the Memory management of Idle VMs.  Each powered on VM incurs Memory Overhead.   The Memory Overhead includes space reserved for the VM frame buffer and various virtualization data structures, such as Shadow Page Tables (using Software Virtualization) or Nested Page Tables (using Hardware Virtualization).  This also depends on the number of vCPUs and the configured memory granted to the VM.

We’ll have a look at a few more reasons to care on Monday, in the meantime why not complete our Capacity Management Maturity Survey and find out where you fall on the maturity scale. http://www.metron-athene.com/_capacity-management-maturity-survey/survey.asp

Jamie Baker

Principal Consultant

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 Capacity Management' taking place on May 25.

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

Jamie Baker

Principal Consultant

Idle VMs - Why should we care? (3 of 3)

Earlier in the week I looked at the impact idle VM’s can have on CPU utilization and memory overhead today I’m going to look at the amount of Disk or Datastore space usage per Idle VM. 

Each one will have associated VMDK (disk) files.  The files are stored within a Datastore, which in most cases is hosted SAN or NAS storage and shared between the cluster host members.  If VMDKs are provisioned as "Thick Disks" then the provisioned space is locked out within the Datastore for those disks.

To illustrate this an example of a least worst case scenario would be:  100 Windows  idle VMs have been identified across the Virtual Infrastructure and each VM has a "Thick" single VMDK of 20GB used to house the operating system.  This would then equate to 2TB of Datastore space being locked for use by VMs that are idle.  You can expand this further by, making an assumption  that some if not all VMs are likely to have more disks and of differing sizes.

The simple math will show you how much Datastore space is being wasted.

There is a counter to this, known as Thin Provisioning.  By using Thin disks, in which the provisioned disk size is reserved but not locked you  would not waste the same amount of space as you would by using Thick Disks.  Using Thin Provisioning also has the added benefit of being able to over allocate disk space thus leading to a reduction in the amount of up front storage capacity required, but only incurring minimal overhead.

Idle VMs -  why you should care.

Identifying Idle VMs, questioning whether they are required, finding out who owns them and  removing them completely will reduce or help eliminate VM sprawl and help to improve the performance and capacity of the Virtual Infrastructure by:

·       reducing unnecessary timer interrupts

·       reducing allocated vCPUs

·       reducing unnecessary CPU and Memory overhead

·       reduce used Datastore space

·       lead to more efficient use of your Virtual Infrastructure, including improved VM to Host ratios and reduction in additional hardware.

Don't forget to sign up for our Capacity Management Maturity online workshop.

http://www.metron-athene.com/services/online-workshops/index.html

Jamie Baker

Principal Consultant

Idle VMs - Why should we care? (2 of 3)

In my previous blog I mentioned the term VM Sprawl and this is where Idle VMs are likely to factor. 

Often VMs are provisioned to support short term projects,  for development/test processes or for applications which have now been decommissioned.  Now idle, they’re left alone, not bothering anyone and therefore not on the Capacity and Performance teams radar.

Which brings us back to the question.  Idle VMs - Why should we care? 

We should care, for a number of reasons but let's start with the impact on CPU utilization.

When VMs are powered on and running, timer interrupts have to be delivered from the host CPU to the VM.  The total number of timer interrupts being delivered depends on the following factors:

·       VMs running symmetric multiprocessing (SMP), hardware abstraction layers (HALs)/kernels require more timer interrupts than those running Uniprocessor HALs/Kernels.

·       How many virtual CPUs (vCPUs) the VM has.

Delivering many virtual timer interrupts can negatively impact on the performance of the VM and can also increase host CPU consumption.  This can be mitigated however, by reducing the number of vCPUs which reduces the timer interrupts and also the amount of co-scheduling overhead (check CPU Ready Time). 

Then there's the Memory management of Idle VMs.  Each powered on VM incurs Memory Overhead.   The Memory Overhead includes space reserved for the VM frame buffer and various virtualization data structures, such as Shadow Page Tables (using Software Virtualization) or Nested Page Tables (using Hardware Virtualization).  This also depends on the number of vCPUs and the configured memory granted to the VM.

We’ll have a look at a few more reasons to care on Wednesday, in the meantime why not complete our Capacity Management Maturity Survey and find out where you fall on the maturity scale. http://www.metron-athene.com/_capacity-management-maturity-survey/survey.asp

Jamie Baker

Principal Consultant

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 Monday.
In the meantime why not register for my webinar VMware Capacity Planning'

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

Jamie Baker

Principal Consultant