Before working on a vSAN environment, you should be aware of the characteristics of a vSAN cluster.
A vSAN cluster includes the following characteristics:
You can have multiple vSAN clusters for each vCenter Server instance. You can use a single vCenter Server to manage more than one vSAN cluster.
vSAN consumes all devices, including flash cache and capacity devices, and does not share devices with other features.
vSAN clusters can include hosts with or without capacity devices. The minimum requirement is three hosts with capacity devices. For best result, create a vSAN cluster with uniformly configured hosts.
If a host contributes capacity, it must have at least one flash cache device and one capacity device.
In hybrid clusters, the magnetic disks are used for capacity and flash devices for read and write cache. vSAN allocates 70 percent of all available cache for read cache and 30 percent of available cache for write buffer. In this configurations, the flash devices serve as a read cache and a write buffer.
In all-flash cluster, one designated flash device is used as a write cache, additional flash devices are used for capacity. In all-flash clusters, all read requests come directly from the flash pool capacity.
Only local or direct-attached capacity devices can participate in a vSAN cluster. vSAN cannot consume other external storage, such as SAN or NAS, attached to cluster.
For best practices about designing and sizing a vSAN cluster, see Designing and Sizing a vSAN Cluster.