Design Considerations for Flash Capacity Devices in vSAN

Plan the configuration of flash capacity devices for vSAN all-flash configurations to provide high performance and required storage space, and to accommodate future growth.

Choosing Between PCIe or SSD Flash Devices

Choose PCIe or SSD flash devices according to the requirements for performance, capacity, write endurance, and cost of the vSAN storage.

• Compatibility. The model of the PCIe or SSD devices must be listed in the vSAN section of the VMware Compatibility Guide.
• Performance. PCIe devices generally have faster performance than SSD devices.
• Capacity. The maximum capacity that is available for PCIe devices is generally greater than the maximum capacity that is currently listed for SSD devices for vSAN in the VMware Compatibility Guide.
• Write endurance. The write endurance of the PCIe or SSD devices must meet the requirements for capacity or for cache in all-flash configurations, and for cache in hybrid configurations.

  For information about the write endurance requirements for all-flash and hybrid configurations, see the VMware vSAN Design and Sizing Guide. For information about the write endurance class of PCIe and SSD devices, see the vSAN section of the VMware Compatibility Guide.

• Cost. PCIe devices generally have higher cost than SSD devices.

Flash Devices as vSAN Capacity

In all-flash configurations, vSAN does not use cache for read operations and does not apply the read-cache reservation setting from the VM storage policy. For cache, you can use a small amount of more expensive flash that has high write endurance. For capacity, you can use flash that is less expensive and has lower write endurance.

Plan a configuration of flash capacity devices by following these guidelines:

• For better performance of vSAN, use more disk groups of smaller flash capacity devices.
• For balanced performance and predictable behavior, use the same type and model of flash capacity devices.