After you enable and configure VMware vSAN for a VI workload domain cluster in VMware Cloud Foundation, you can create storage policies that define the virtual machine storage characteristics. Storage characteristics specify different levels of service for different virtual machines.

Policy design starts with assessment of business needs and application requirements. Assess the use cases for VMware vSAN to determine the necessary policies. Start by assessing the following application requirements:

  • I/O performance and profile of your workloads on a per-virtual-disk basis
  • Working sets of your workloads
  • Hot-add of additional cache (requires repopulation of cache)
  • Specific application best practice, such as block size

After assessment, configure the software-defined storage module policies for availability and performance in a conservative manner so that space consumed and recoverability properties are balanced. Usually the default system policy covers most common cases. You create custom policies if specific requirements for performance or availability exist.

If you do not specify a user-configured policy, vSAN uses a default system policy of 1 failure to tolerate and 1 disk stripe for virtual machine namespace and virtual disks. To ensure protection for critical virtual machine components, vSAN uses the policy set on virtual machine namespace for swap files. vSAN also uses the policy set on the virtual disk for the associated snapshot delta disks, if exist.

Object

Policy

Comments

Virtual machine namespace

User-configured storage policy

Can be any storage policy configured on the system.

Swap

Uses virtual machine namespace policy

Same as Virtual machine namespace policy.

Virtual disks

User-configured storage policy

Can be any storage policy configured on the system.

Virtual disk snapshots

Uses virtual disk policy

Same as virtual disk policy.
Table 1. Design Decisions on the vSAN Storage Policy in a VI Workload Domain with a Single Availability Zone

Decision ID

Design Decision

Design Justification

Design Implication

VCF-WLD-vSAN-CFG-008

Use the default vSAN storage policy.

Provides the level of redundancy that is needed in the VI workload domain cluster.

Provides the level of performance that is enough for NSX Edge appliances and tenant workloads.

You might need additional policies for third-party virtual machines hosted in the VI workload domain cluster because their performance or availability requirements might differ from what the default vSAN policy supports.
Table 2. Design Decisions on the vSAN Storage Policy in a VI Workload Domain with Multiple Availability Zones

Decision ID

Design Decision

Design Justification

Design Implication

VCF-WLD-vSAN-CFG-009

Add the following setting to the default vSAN storage policy:

Secondary Failures to Tolerate = 1

Provides the necessary protection for virtual machines in each availability zone, with the ability to recover from an availability zone outage.

You might need additional policies if third-party virtual machines are to be hosted in the VI workload domain cluster because their performance or availability requirements might differ from what the default vSAN policy supports.

VCF-WLD-vSAN-CFG-010

Configure two fault domains, one for each availability zone. Assign each host to their respective availability zone fault domain.

Fault domains are mapped to availability zones to provide logical host separation and ensure a copy of vSAN data is always available even when an availability zone goes offline.

Additional raw storage is required when the secondary failures to tolerate option and dault domains are enabled.