vSphere DRS Design for a Virtual Infrastructure Workload Domain

vSphere Distributed Resource Scheduling (vSphere DRS) provides load balancing in a cluster by migrating workloads from heavily loaded ESXi hosts to ESXi hosts with more available resources in the cluster.

vSphere DRS supports the following automation modes.

Table 1. vSphere DRS Automation Modes

Automation Mode	Description
Manual	vSphere DRS provides recommendations, but an administrator must confirm the changes.
Partially Automated	vSphere DRS provides recommendations to migrate virtual machines to fulfill certain criteria and an administrator must confirm the changes. vSphere DRS automatically places virtual machines on hosts with sufficient resources at power-on operations.
Fully Automated	vSphere DRS automatically migrates VMs to fulfill certain criteria and automatically places workloads onto appropriate hosts at power-on operations.

When using two availability zones, create VM-Host group affinity rules for initial placement of virtual machines. These affinity rules ensure that virtual machines run in a single availability zone unless an outage event occurs. In this way, you avoid unnecessary vSphere vMotion migrations of virtual machines between availability zones.

Table 2. Design Decisions on vSphere DRS in a VI Workload Domain with a Single Availability Zone

Decision ID	Design Decision	Design Justification	Design Implication
VCF-WLD-VCS-CLS-014	Enable vSphere DRS on all clusters, using the default fully automated mode with medium threshold.	Provides the best trade-off between load balancing and unnecessary migrations with vSphere vMotion.	If a vCenter Server outage occurs, the mapping from virtual machines to ESXi hosts might be difficult to determine.

Table 3. Design Decisions on vSphere DRS in a VI Workload Domain with Multiple Availability Zones

Decision ID	Design Decision	Design Justification	Design Implication
VCF-WLD-VCS-CLS-015	Create a host group for each availability zone and add the ESXi hosts in the zone to the respective group.	Makes it easier to manage which virtual machines run in which availability zone.	You must create and maintain VM-Host DRS group rules.
VCF-WLD-VCS-CLS-016	Create a virtual machine group for each availability zone and add the VMs in the zone to the respective group.	Ensures that virtual machines are located only in the assigned availability zone to avoid unnecessary vSphere vMotion operations.	You must add virtual machines to the allocated group manually.
VCF-WLD-VCS-CLS-017	Create a should-run VM-Host affinity rule to run each group of virtual machines on the respective group of hosts in the same availability zone.	Ensures that virtual machines are located only in the assigned availability zone to avoid unnecessary vSphere vMotion migrations.	You must manually create the rules.