Installation guide

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VMware ESX Server Administration Guide
For example, if one of your virtual machines is running an important application, you
can specify a higher minimum percentage for this virtual machine, compared to the
other virtual machines on your ESX Server.
Note: You can set CPU percentages for some, or all of your virtual machines.
Alternately, you may choose to set only minimum, or only maximum CPU
percentages. You do not need to set both.
For example, you plan to run 20 virtual machines on your ESX Server machine, but
have currently deployed only five virtual machines. Normally, these five virtual
machines would utilize any extra CPU time that is available on the ESX Server
machine. However, after you deploy an additional 15 virtual machines, these five initial
virtual machines will receive a smaller share of CPU time, than what they were used to
previously.
If you prefer not to have the users of these original five virtual machines become
accustomed to this higher level of CPU time, you could set a maximum CPU
percentage for these five virtual machines and limit the amount of CPU time they
receive. Then, these users won’t see a difference when you deploy the additional
virtual machines.
Note: The CPU percentage(s) you choose represent an absolute fixed limit for that
virtual machine.
Assigning Virtual Machines to Run on Specific Processors
In multiprocessor systems, you can also restrict the assignment of virtual machines to
a subset of the available processors by specifying an affinity set for each virtual
machine. The system automatically assigns each virtual machine to processors in the
specified affinity set in order to achieve the CPU allocations specified by the
minimum, maximum and shares settings associated with each virtual machine. If the
affinity set for a uniprocessor virtual machine contains only a single processor, then
the virtual machine is placed there.
As mentioned previously, the scheduler performs automatic load balancing of CPU
time. To optimize this automatic load balancing, you should avoid manually
specifying affinity for a virtual machine. Instead, we suggest setting a CPU minimum
to guarantee the minimal acceptable performance for a virtual machine.
Note: By specifying a minimum (instead of specifying affinity), ESX Server has the
maximum flexibility for automatic optimizations.
For more information, see Managing CPU Resources from the Management Interface
on page 394.