5.5

Table Of Contents
Configuring Virtual Machine Resource Allocation Settings
Reservation pool virtual datacenters support the ability to control resource allocation at the virtual machine
level. Users with the necessary rights can customize the amount of resources that are allocated to their
virtual machines.
Use the resource allocation settings (shares, reservation, and limit) to determine the amount of CPU,
memory, and storage resources provided for a virtual machine. Users have several options for allocating
resources.
n
Ensure that a certain amount of memory for a virtual machine is provided by the virtual datacenter.
n
Guarantee that a particular virtual machine is always allocated a higher percentage of the virtual
datacenter resources than other virtual machines.
n
Set an upper bound on the resources that can be allocated to a virtual machine.
Resource Allocation Shares
Shares specify the relative importance of a virtual machine within a virtual datacenter. If a virtual machine
has twice as many shares of a resource as another virtual machine, it is entitled to consume twice as much of
that resource when these two virtual machines are competing for resources.
Shares are typically specified as High, Normal, or Low and these values specify share values with a 4:2:1
ratio, respectively. You can also select Custom to assign a specific number of shares (which expresses a
proportional weight) to each virtual machine.
When you assign shares to a virtual machine, you always specify the priority for that virtual machine
relative to other powered-on virtual machines.
The following table shows the default CPU and memory share values for a virtual machine.
Table 82. Share Values
Setting CPU share values Memory share values
High 2000 shares per virtual CPU 20 shares per megabyte of configured virtual
machine memory.
Normal 1000 shares per virtual CPU 10 shares per megabyte of configured virtual
machine memory.
Low 500 shares per virtual CPU 5 shares per megabyte of configured virtual machine
memory.
For example, a virtual machine with two virtual CPUs and 1GB RAM with CPU and memory shares set to
Normal has 2x1000=2000 shares of CPU and 10x1024=10240 shares of memory.
The relative priority represented by each share changes when a new virtual machine is powered on. This
affects all virtual machines in the same virtual datacenter.
Resource Allocation Reservation
A reservation specifies the guaranteed minimum allocation for a virtual machine.
vCloud Director allows you to power on a virtual machine only if there are enough unreserved resources to
satisfy the reservation of the virtual machine. The virtual datacenter guarantees that amount even when its
resources are heavily loaded. The reservation is expressed in concrete units (megahertz or megabytes).
vCloud Director User's Guide
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