6.7

Table 10‑1. Reservation Types
Reservation Type Description
Fixed The system checks whether the selected resource pool has sufficient unreserved resources. If
it does, the action can be performed. If it does not, a message appears and the action cannot
be performed.
Expandable
(default)
The system considers the resources available in the selected resource pool and its direct
parent resource pool. If the parent resource pool also has the Expandable Reservation
option selected, it can borrow resources from its parent resource pool. Borrowing resources
occurs recursively from the ancestors of the current resource pool as long as the Expandable
Reservation option is selected. Leaving this option selected offers more flexibility, but, at the
same time provides less protection. A child resource pool owner might reserve more resources
than you anticipate.
The system does not allow you to violate preconfigured Reservation or Limit settings. Each time you
reconfigure a resource pool or power on a virtual machine, the system validates all parameters so all
service-level guarantees can still be met.
Expandable Reservations Example 1
This example shows you how a resource pool with expandable reservations works.
Assume an administrator manages pool P, and defines two child resource pools, S1 and S2, for two
different users (or groups).
The administrator knows that users want to power on virtual machines with reservations, but does not
know how much each user will need to reserve. Making the reservations for S1 and S2 expandable
allows the administrator to more flexibly share and inherit the common reservation for pool P.
Without expandable reservations, the administrator needs to explicitly allocate S1 and S2 a specific
amount. Such specific allocations can be inflexible, especially in deep resource pool hierarchies and can
complicate setting reservations in the resource pool hierarchy.
Expandable reservations cause a loss of strict isolation. S1 can start using all of P's reservation, so that
no memory or CPU is directly available to S2.
Expandable Reservations Example 2
This example shows how a resource pool with expandable reservations works.
Assume the following scenario, as shown in the figure.
n
Parent pool RP-MOM has a reservation of 6GHz and one running virtual machine VM-M1 that
reserves 1GHz.
n
You create a child resource pool RP-KID with a reservation of 2GHz and with Expandable
Reservation selected.
n
You add two virtual machines, VM-K1 and VM-K2, with reservations of 2GHz each to the child
resource pool and try to power them on.
n
VM-K1 can reserve the resources directly from RP-KID (which has 2GHz).
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VMware, Inc. 67