VMware vSphere vCenter Server 4.0 - Manual (Page 16)

Table 1-9. Resource Settings
Field Description
Reservation Guaranteed memory allocation for this virtual machine.
Limit Upper limit for this virtual machine’s memory allocation.
Shares Memory shares for this virtual machine.
Configured User-specified guest physical memory size.
Worst Case
Allocation
The amount of (CPU or memory) resource that is allocated to the virtual machine based on user-
configured resource allocation policies (for example, reservation, shares and limit), and with the
assumption that all virtual machines in the cluster consume their full amount of allocated resources.
Overhead
Reservation
The amount of memory that is being reserved for virtualization overhead.
Admission Control
When you power on a virtual machine, the system checks the amount of CPU and memory resources that have
not yet been reserved. Based on the available unreserved resources, the system determines whether it can
guarantee the reservation for which the virtual machine is configured (if any). This process is called admission
control.
If enough unreserved CPU and memory are available, or if there is no reservation, the virtual machine is
powered on. Otherwise, an
Insufficient Resources
warning appears.
N
OTE
In addition to the user-specified memory reservation, for each virtual machine there is also an amount
of overhead memory. This extra memory commitment is included in the admission control calculation.
When the VMware DPM feature is enabled, hosts might be placed in standby mode (that is, powered off) to
reduce power consumption. The unreserved resources provided by these hosts are considered available for
admission control. If a virtual machine cannot be powered on without these resources, a recommendation to
power on sufficient standby hosts is made.
vSphere Resource Management Guide
16 VMware, Inc.