Finalized Cluster and Disk Group Design
This section provides different decision points to aid in the design of the cluster and disk groups for Virtual SAN.
Size of the Virtual SAN Datastore
Given all the variables mentioned, the end size of the Virtual SAN datastore is based on the requirements for the datastore. Thus, cost versus availability must be considered to provide the appropriate sizing for the datastore.
Table 66. Virtual SAN Datastore Selection – Design Decisions
| Decision ID | Design Decision | Design Justification | Design Implication |
|---|---|---|---|
| For this design, <Customer> has made the following decisions listed in this table. | |||
Number of Hosts Per Cluster
To reach the target size for the volume as listed in the previous section, the number of hosts that are required in the cluster is a consideration based on the following:
Amount of available space on the Virtual SAN datastore.
Number of available failures you wish to tolerate in the cluster.
The number of hosts is generally a balance between hardware and space.
More ESXi hosts and/or disk groups means higher hardware costs.
Fewer ESXi hosts and/or disk groups means resource availability could suffer.
For example, if the Virtual SAN cluster has only three ESXi hosts, only a single failure is supported. If a higher level of availability is required, additional hosts are also required.
Table 67. Number of Hosts Per Cluster
| Design Quality | Option 1 | Option 216 Hosts | Option 3 | Comments |
|---|---|---|---|---|
| Availability | ↓ | ↑ | ↑↑ | The more hosts that are available in the cluster, the more failures are tolerated in the cluster. |
| Manageability | ↓ | ↑ | ↑ | The more hosts in the cluster, the more virtual machines that can be managed in the Virtual SAN environment. |
| Performance | ↑ | ↓ | ↓ | The larger cluster (although it is more available) can impact the performance of the environment if there is an imbalance of resources. In this case, special caution should be taken to prevent issues. |
| Recoverability | o | o | o | Neither design option impacts recoverability. |
| Security | o | o | o | Neither design option impacts security. |
Legend: ↑ = positive impact on quality; ↓ = negative impact on quality; o = no impact on quality.
Table 68. Cluster Size Selection – Design Decisions
| Decision ID | Design Decision | Design Justification | Design Implication |
|---|---|---|---|
| For this design, <Customer> has made the following decisions listed in this table. | |||
| The clusters for Virtual SAN will have 4 hosts. |
Number of Disk Groups Per Host
Disk group sizing is also an important factor to consider when designing the volume. Include the following data points when deciding on the number of disk groups per host:
Amount of available space on the Virtual SAN datastore
Number of available failures you want to tolerate in the cluster
The optimal number of disk groups is a balance between hardware and space requirements for the Virtual SAN datastore. More disk groups increase space and provide higher availability. However, adding disk groups may be cost-prohibitive.
The recommended configuration for the Software-Defined Storage moduleis to utilize two disk groups per host, containing 3 HDDs. This means that each host contains two SSDs and six HDDs. However, based on sizing calculations listed in Section 8.3.3, Datastore Sizing, you can use more or fewer disks to meet the sizing requirements for Virtual SAN (and the estimated sizing required for the overall design).
Table 69. Number of Disk Groups Per Host
| Design Quality | Option 1 | Option 2 | Option 3 | Comments |
|---|---|---|---|---|
| Availability | ↓ | ↑ | ↑↑ | If more hosts are available in the cluster, more failures are tolerated in the cluster. This capability adds cost because additional hardware for the disk groups is required. |
| Manageability | o | o | o | If more hosts are in the cluster, more virtual machines can be managed in the Virtual SAN environment. |
| Performance | o | ↑ | ↑↑ | If the flash percentage ratio to storage capacity is large, Virtual SAN can deliver increased performance and speed. |
| Recoverability | o | o | o | More available disk groups can increase the recoverability of Virtual SAN during a failure. |
| Security | o | o | o | Neither design option impacts security. |
Legend: ↑ = positive impact on quality; ↓ = negative impact on quality; o = no impact on quality.
Table 70. Disk Groups Per Host Selection – Design Decisions
| Decision ID | Design Decision | Design Justification | Design Implication |
|---|---|---|---|
| For this design, <Customer> has made the following decisions listed in this table. | |||