Doing the math for hypervisor memory overhead, Hp virtual machine, Vmware esx 3 – HP Matrix Operating Environment Software User Manual
Page 129: Vmware vsphere, Microsoft hyper-v
Where you might use this percentage adjustment
•
when moving workloads from one system platform to another different system platform in a
scenario, where one or both system platforms are VM hosts.
Doing the math for hypervisor memory overhead
When you encounter this adjustment factor in altering a scenario, you have a choice to supply
your own values. To help you with this, the following calculation examples are provided.
HP Virtual Machine
To compute the memory overhead of the hypervisor, use the following formula:
750 MB (.73 GB) + 7.5% of (Total Physical Memory – 1 GB)
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:
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 web site.
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 (2 VCPUS) in the table at this location:
For more information, see the appropriate Resource Management Guide on the VMware web site.
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 2 guests with 2 GB of RAM, and 2 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
on Hyper-V hosts.
Source:
on the Windows Hardware
Developer Central web site.
Adjusting for virtualization changes
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