Jersey Datacentre and Cloud Services Knowledgebase (previously provided by Foreshore)

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vCloud Director Memory Overhead

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vCloud Director Memory Overhead

Virtualization of memory resources has some associated overhead.  The memory space overhead has two components.

  •    A fixed, system-wide overhead for the VMkernel.
  •   Additional overhead for each virtual machine.


Overhead memory includes space reserved for the virtual machine frame buffer and various virtualization data structures, such as shadow page tables. Overhead memory depends on the number of virtual CPUs and the configured memory for the guest operating system.

Because Allocation model customers are unable to oversubscribe their purchased resources, Allocation model Virtual Datacentres are configured with more memory than has been purchased and this will appear in the vCloud Director Administrator console. Foreshore estimates this memory overhead based on the memory purchased and allocates this in addition to the purchased amount. Increasing the memory limit to allow for the overhead allows customers to allocate and power on the amount of memory purchased. Customers should not allocate and attempt to power on more memory than has been purchased (even though the vCloud Director GUI shows a higher amount) as VMs will be prevented from powering on because the memory is not available, albeit appearing available in the vCloud Director GUI.

For example:

Purchased memory  - 10  GB

vCloud shows – 11 GB

Although vCloud shows 11 GB customers should only use up to their purchased 10 GB  (5 VM’s at 2GB each for example).

If you are unsure on how much memory you have purchased please contact and our team will be happy to help.

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Last Modified:01/08/2014 16:00:19

Last Modified By: joes

Type: FAQ

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