VMware vSphere vCenter Server 4.0 - Manual (Page 60)

Figure 6-2. Valid Cluster with Expandable Resource Pools
cluster
Total Capacity: 16G
Reserved Capacity: 16G
Available Capacity: 0G
RP1 (expandable)
Reservation: 4G
Reservation Used: 6G
Unreserved: 0G
RP2
Reservation: 5G
Reservation Used: 3G
Unreserved: 2G
RP3 (expandable)
Reservation: 5G
Reservation Used: 5G
Unreserved: 0G
VM1, 2G
VM7, 2G
VM2, 2G
VM4, 1G VM8, 2G
VM3, 3G VM5, 2G VM6, 2G
A valid cluster can be configured as follows:
n A cluster with total resources of 16GHz.
n RP1 and RP3 are of type Expandable, RP2 is of type Fixed.
n The total reservation used of the three resource pools combined is 16GHz (6GHz for RP1, 5GHz for RP2,
and 5GHz for RP3). 16GHz shows up as the Reserved Capacity for the cluster at top level.
n RP1 was created with a reservation of 4GHz. Three virtual machines of 2GHz each are powered on. Two
of those virtual machines (for example, VM1 and VM7) can use RP1’s reservations, the third virtual
machine (VM6) can use reservations from the cluster’s resource pool. (If the type of this resource pool
were Fixed, you could not power on the additional virtual machine.)
n RP2 was created with a reservation of 5GHz. Two virtual machines of 1GHz and 2GHz are powered on
(Reservation Used: 3GHz). 2GHz remains unreserved.
RP3 was created with a reservation of 5GHz. Two virtual machines of 3GHz and 2GHz are powered on.
Even though this resource pool is of type Expandable, no additional 2GHz virtual machine can be powered
on because the parent’s extra resources are already used by RP1.
Overcommitted DRS Clusters
A cluster becomes overcommitted (yellow) when the tree of resource pools and virtual machines is internally
consistent but the cluster does not have the capacity to support all resources reserved by the child resource
pools.
There will always be enough resources to support all running virtual machines because, when a host becomes
unavailable, all its virtual machines become unavailable. A cluster typically turns yellow when cluster capacity
is suddenly reduced, for example, when a host in the cluster becomes unavailable. VMware recommends that
you leave adequate additional cluster resources to avoid your cluster turning yellow.
Consider the following example, as shown in
Figure 6-3 .
vSphere Resource Management Guide
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