VMware vSphere vCenter Server 4.0 - Manual (Page 58)

DRS Cluster Validity
The vSphere Client indicates whether a DRS cluster is valid, overcommitted (yellow), or invalid (red).
DRS clusters become overcommitted or invalid for several reasons.
n A cluster might become overcommitted if a host fails.
n A cluster becomes invalid if vCenter Server is unavailable and you power on virtual machines using a
vSphere Client connected directly to an ESX/ESXi host.
n A cluster becomes invalid if the user reduces the reservation on a parent resource pool while a virtual
machine is in the process of failing over.
n If changes are made to hosts or virtual machines using a vSphere Client connected to an ESX/ESXi host
while vCenter Server is unavailable, those changes take effect. When vCenter Server becomes available
again, you might find that clusters have turned red or yellow because cluster requirements are no longer
met.
When considering cluster validity scenarios, you should understand these terms.
Reservation A fixed, guaranteed allocation for the resource pool input by the user.
Reservation Used The sum of the reservation or reservation used (whichever is larger) for each
child resource pool, added recursively.
Unreserved This nonnegative number differs according to resource pool type.
Table 6-1. Resource Pool Unreserved Numbers
Resource Pool Type Number Used
Nonexpandable resource pools Reservation minus reservation used.
Expandable resource pools (Reservation minus reservation used) plus any unreserved
resources that can be borrowed from its ancestor resource
pools.
Valid DRS Clusters
A valid cluster has enough resources to meet all reservations and to support all running virtual machines.
Figure 6-1 shows an example of a valid cluster with fixed resource pools and how its CPU and memory
resources are computed.
vSphere Resource Management Guide
58 VMware, Inc.