vSAN Storage Policy Design for the Management Domain

After you enable and configure VMware vSAN 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.

Configure policies according to the business requirements of the application. By using policies, vSAN can adjust the performance and the availability of a disk on the fly.

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 consumed space and recoverability 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.

Table 1. vSAN Policies

Object Type	Policy	Comments
Virtual machine namespace	User-configured storage policy	Can be any storage policy configured on the system.
Swap	Uses the virtual machine namespace policy	Same as the virtual machine namespace policy.
Virtual disks	User-configured storage Policy	Can be any storage policy configured on the system.
Virtual disk snapshots	Uses the virtual disk policy	Same as the virtual disk policy.

Table 2. Design Decisions on the vSAN Storage Policy in a Management Domain with a Single Availability Zone

Decision ID	Design Decision	Design Justification	Design Implication
VCF-MGMT-VSAN-CFG-013	Use the default VMware vSAN storage policy.	Provides the level of redundancy that is needed in the management cluster. Provides the level of performance that is enough for the individual management components.	You might need additional policies for third-party virtual machines hosted in these clusters because their performance or availability requirements might differ from what the default VMware vSAN policy supports.
VCF-MGMT-VSAN-CFG-014	Leave the default virtual machine swap file as a sparse object on VMware vSAN.	Sparse virtual swap files only consume capacity on vSAN as they are accessed. As a result, you can reduce the consumption on the vSAN datastore if virtual machines do not experience memory over-commitment which requires the use of the virtual swap file.	None.

Table 3. Design Decisions on the vSAN Storage Policy in a Management Domain with Multiple Availability Zones

Decision ID	Design Decision	Design Justification	Design Implication
VCF-MGMT-VSAN-CFG-015	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 these clusters because their performance or availability requirements might differ from what the default VMware vSAN policy supports.
VCF-MGMT-VSAN-CFG-016	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 failure to tolerate option and fault domains are enabled.