Dynamic Optimization and Resource Balancing
When a virtual machine is created with SCVMM to a cluster, each node is given a star
rating based on its suitability to host the new virtual machine, and one of the criteria
is the host’s current utilization. Over time, as new virtual machines are created, your
cluster may become uneven, with some hosts running many more virtual machines
than others.
Dynamic Optimization (DO) was a new feature in SCVMM 2012 that was designed to
ensure that the hosts within a cluster (Hyper-V, ESX, or XenServer) were spreading
the virtual machine load as evenly as possible, avoiding certain hosts being heavily
loaded (potentially affecting the performance of virtual machines) while other hosts
were fairly lightly loaded. Dynamic Optimization is one of the most used features in
almost all virtualized environments because of the dynamic balancing of virtual
machines and because it removes a lot of the manual activities required of
administrators around the placement of virtual machines. It is important to note that
no amount of dynamic balancing can compensate for a poorly architected or
overloaded environment, and it’s still critical to perform accurate discovery and design
of virtual environments.
DO is not considered a replacement for Performance Resource Optimization (PRO),
which was present in SCVMM 2008 and leveraged System Center Operations Manager
for detail on utilization of the environment. Instead, DO is considered a
complementary technology that does not rely on Operations Manager and is seen very
much as a reactive technology. DO works by periodically looking at the resource
utilization of each host in a cluster, and if the utilization drops below defined levels, a
rebalancing of the virtual machines is performed to better equalize host utilization
throughout the cluster. As Figure 7.39 shows, thresholds for CPU, memory, disk, and
network can be defined in addition to how aggressive the rebalancing will be. The
more aggressive it is, the quicker DO will be to move virtual machines for even a small
gain in performance, which means more Live Migrations.