The cluster design must consider the characteristics of the workloads deployed in the VI workload domain.

When you design the cluster layout in vSphere, consider the following guidelines:

  • Use fewer, larger ESXi hosts, or more, smaller ESXi hosts.

    • A scale-up cluster has fewer, larger ESXi hosts.

    • A scale-out cluster has more, smaller ESXi hosts.

  • Compare the capital costs of purchasing fewer, larger ESXi hosts with the costs of purchasing more, smaller ESXi hosts. Costs vary between vendors and models. Evaluate the risk of losing one larger host in a scale-up cluster and the impact on the business with the higher change to lose one or more small hosts in scale-out cluster.

  • Evaluate the operational costs for managing a few ESXi hosts with the costs of managing more ESXi hosts.

  • Consider the purpose of the cluster.

  • Consider the total number of ESXi hosts and cluster limits.

Figure 1. vSphere Logical Cluster Layout with a Single Availability Zone

In an SDDC, for a setup with one availability zone, you organize management workloads in the default management cluster and customer workloads and NSX Edge appliances in a shared edge and workload cluster of the VI workload domain.

Figure 2. vSphere Logical Cluster Layout with Two Availability Zones
In an SDDC, for a setup with two availability zones, you organize management workloads in a stretched vSAN cluster in the management domain and customer workloads and edge devices in a stretched shared edge and workload cluster in the VI workload domain.
Table 1. Number of Hosts in a VI Workload Domain Cluster with vSAN as Principal Storage

Attribute

Specification

Minimum number of ESXi hosts required for a VI workload domain cluster

Single availability zone

4

Two availability zones

8

Reserved capacity for handling ESXi host failures per cluster

Single availability zone

25% CPU and RAM

Tolerates one host failure

Two availability zones

50% CPU and RAM

Tolerates one availability zone failure

Table 2. Number of Hosts in a VI Workload Domain Cluster with vVols, NFS, or VMFS on FC as Principal Storage

Attribute

Specification

Minimum number of ESXi hosts required for a VI workload domain cluster

Single availability zone

3

Two availability zones

6

Reserved capacity for handling ESXi host failures per cluster

Single availability zone

33% CPU and RAM

Tolerates one host failure.

Two availability zones

50% CPU and RAM

Tolerates one availability zone failure.

Table 3. Design Decisions on the Cluster Configuration in a VI Workload Domain with a Single Availability Zone

Decision ID

Design Decision

Design Justification

Design Implication

VCF-WLD-VCS-CLS-001

Create a shared edge and workload vSphere cluster in the VI workload domain.

  • Simplifies configuration by isolating tenant workloads from management workloads.

  • Ensures that management workloads have no impact on tenant workloads.

You can add ESXi hosts to the cluster as needed.

Management of multiple clusters and vCenter Server instances increases operational overhead.

VCF-WLD-VCS-CLS-002

If using vSAN as the principal storage, create the shared edge and workload cluster in the VI workload domain with a minimum of 4 ESXi hosts.

  • Allocating 4 ESXi hosts provides N+1 redundancy for the cluster to protect against host failure.

  • Having 4 ESXi hosts also guarantees vSAN and NSX-T Data Center redundancy during availability zone outages or maintenance operations.

To support redundancy, you must allocate additional ESXi host resources.

Table 4. Design Decisions on the Cluster Configuration in a VI Workload Domain with Multiple Availability Zones

Decision ID

Design Decision

Design Justification

Design Implication

VCF-WLD-VCS-CLS-003

Add 4 ESXi hosts to create the second availability zone of a shared edge and workload cluster in the VI workload domain. The total number of ESXi hosts in the shared edge and workload cluster of the VI workload domain across the two availability zones is eight.

  • Allocating 4 ESXi hosts provides N+1 redundancy for each availability zone in the cluster to protect against host failure.

  • Having 4 ESXi hosts in each availability zone guarantees vSAN and NSX-T Data Center redundancy during availability zone outages or maintenance operations.

To support redundancy, you must allocate additional ESXi host resources.

Table 5. Design Decisions on the Configuration for a VI Workload Domain Cluster for Multiple VMware Cloud Foundation Instances

Decision ID

Design Decision

Design Justification

Design Implication

VCF-WLD-VCS-CLS-004

In each additional VMware Cloud Foundation instance, create the shared edge and workload cluster in the VI workload domain with a minimum of 4 ESXi hosts, when using vSAN as the principal storage.

  • Allocating 4 ESXi hosts provides N+1 redundancy for the cluster.

  • Having 4 ESXi hosts guarantees vSAN and NSX redundancy during maintenance operations.

To support redundancy, you must allocate additional ESXi host resources .