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run on different servers. You can use this to avoid a single point of failure and increase avail-
ability for application components such as web servers in a load-balanced farm.
VMware DRS will help you to load balance the resource utilization across various ESX servers
within resource pools. It continuously monitors utilization across resource pools and then gen-
erates recommendations to optimally place virtual machines within these resource pools. While
doing this, DRS also takes into account any priority settings, such as shares, reservations, and
limits, as well as resource allocation rules and policies you may have defined. You can configure to
execute these virtual machine placement recommendations automatically or manually (Figure 1.6).
VMware DRS does this smart resource allocation during the initial virtual machine placement and
on continuous basis in real time while the virtual machine is running:
Initial placement When a virtual machine is first powered on, VMware DRS either places
the virtual machine on the most appropriate ESX server automatically or makes a recommen-
dation for you to act on.
Continuous optimization The virtual machine resource requirements change over time, and
VMware DRS dynamically responds to these changing needs by migrating virtual machines
between ESX servers using VMware VMotion without disrupting end users. Alternatively, you
can configure DRS to use manual mode so it only makes recommendations that you can then
choose to act on.
By leveraging VMotion, VMware DRS also simplifies planned maintenance on physical servers
without disrupting virtual machines and end users. When you place a physical server in main-
tenance mode, VMware DRS identifies alternative servers where the virtual machines can run.
Based on the automation mode settings, either the virtual machines are automatically moved to
use the alternative servers or the system administrator performs the move manually using the
VMware DRS recommendations as a guideline.
Figure 1.5
VMware vSphere
DRS rules
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