HP Capacity Advisor 7.2 User Guide

Example: For a host with 32 GB of physical memory, the Hypervisor Memory Overhead will be:
750 MB (.73 GB) + 7.5% of 31 GB = .73 GB + 2.24 GB = 2.97 GB
Source: System Sizing Guidelines for Integrity Virtual Machines Deployment
VMware ESX 3
To compute the memory overhead of the hypervisor, use the following formula:
Total Physical Memory – (Total Physical Memory – 284 MB)/1.078
This formula is derived from a least squares fit of observed values in test systems running VMware
ESX. VMware documentation provides tables that outline how much memory overhead to expect
based on the number of virtual CPUs and the amount of memory allocated to guests.
For more information, see the appropriate Resource Management Guide on the VMware website.
VMware vSphere
Capacity Advisor uses the same hypervisor overhead calculation for both ESX 4 and ESX 5 software.
To compute a conservative estimate of the memory overhead of the hypervisor, use a value from
column 3 (two vCPUS) in the table at this location:
Overhead Memory on Virtual Machines
For more information, see the appropriate Resource Management Guide on the VMware website.
Microsoft Hyper-V
Microsoft recommends at least 512 MB (.5 GB) of physical memory be available for basic hypervisor
features.
In addition, for each guest, plan on 32 MB of overhead for the first GB of RAM allocated to a
guest, and 8 MB for each additional GB of RAM allocated to a guest.
To compute the memory overhead introduced by the hypervisor, use the following formula:
512 MB + (Number of Guests x (32 MB for first GB of guest RAM + 8 MB per additional GB of
guest RAM))
Example: For a system hosting two guests with 2 GB of RAM, and two guests with 1 GB of RAM,
the Hypervisor Memory Overhead is as follows:
512 MB + (32 MB + 8 MB) + (32 MB + 8MB) + 32 MB + 32 MB =
512 MB + 40 MB + 40 MB + 32 MB + 32 MB =
656 MB (.64 GB)
Capacity Advisor assumes that a host will be filled with 1 GB guests when estimating the memory
overhead for Hyper-V. This provides a generous estimate of memory overhead, as this configuration
will maximize the size of the memory overhead. As a result, allowing Capacity Advisor to estimate
the Hypervisor Memory Overhead for Hyper-V will leave extra headroom on Hyper-V hosts.
Source: Performance Tuning Guidelines for Windows Server 2008 on the Windows Hardware
Developer Central website.
Power calibration calculations
Manual calibration uses CPU utilization data to estimate power utilization. Power utilization can
be estimated by looking at CPU utilization because power utilization is closely related to CPU
utilization. Further, the greater the CPU usage, the more power that is required to run and cool the
system.
Within the power calibration screens, you can specify the idle and maximum power usage values
that you want to use for power usage calculations. The values can be determined by checking
model and hardware configuration information. For your convenience, HP provides power
calculators to aid you in this process (noted below). Each power calculator allows for different
hardware configurations, such as amount of processors and memory, in order to yield the most
accurate results.
Power calibration calculations 189