HP Matrix 7.2 KVM Private Cloud Getting Started Guide

Table 10 Resource oversubscription rates
Physical to virtual oversubscription rateVirtual resourcePhysical resource
1:88 CPU cores1 CPU core
1:1.51.5 GB RAM1 GB RAM
1:1.51.5 GB disk1 GB disk
A practical example of calculating cloud resources for VM replacement
The purpose of this example is to apply the information provided in the previous section to a realistic
expansion scenario. This section contains a real-world example of how to calculate cloud resources
when replacing VMs that are running on older hardware.
Scenario
There are 400 VMs running on older hardware, which must be moved to a new HP Matrix KVM
Private Cloud. Within the cloud, there are three configurations: small, medium and large. You must
decide where the 400 VMs fit within the three configurations as they move into the cloud.
Determine corresponding VM size configuration
If the existing 400 VMs are currently managed by Matrix OE, you can generate a report using
the Capacity Advisor Reports menu to view the current size and data usage of the VMs. That
information can then be used to decide if the new VMs should be small, medium or large in size.
Refer to the HP Capacity Advisor 7.2 User Guide at http://www.hp.com/go/matrixoe/docs for
more information.
Calculate the number of cores required
The number of cores required corresponds to the size of the VM. A small VM might require one
core, a medium VM might have two cores and a large VM might have four cores. In our scenario,
assume that you need:
• 200 small VMs (200x1)
• 150 medium VMs (150x2)
• 50 large VMs (50x4)
The total number of virtual cores is 700. The Matrix KVM Private Cloud uses an oversubscription
ratio of 1:8 for CPU cores, so you need to have at least 700/8 or 88 cores in the private cloud
to host the VMs. Attempting to use fewer cores will result in a situation in which the cloud is full,
and VMs cannot be created.
Using more cores than required results in additional cost, but will give better performance. If you
anticipate that the physical usage of the cores will be greater than 70% at peak hours, then adding
more cores to your cloud is a good investment. This value can be estimated using Capacity Advisor
if the current VMs are managed by Matrix OE.
Calculate the amount of memory required
When calculating memory, the following guidelines apply to VM size:
• 1 GB of RAM for small VMs (200*1)
• 4 GB of RAM for medium VMs (150*4)
• 8 GB of RAM for large VMs (50*8)
The total amount of memory is 1200 GB of virtual RAM. With an oversubscription ratio of 1:1.5,
you will need to have a minimum of 1200/1.5 or 800 GB of physical RAM in your Matrix KVM
Private Cloud. If you provide less than 800GB then you will not be allowed to create all of the
VMs. While the oversubscription ratio is conservative, there might be VMs that have performance
A practical example of calculating cloud resources for VM replacement 21