The Original vSAN Architecture is a two-tier model that is built on the foundation of disk groups.
A disk group consists of a single cache drive that is partnered with one or more capacity drives. A collection of disk groups is used to form a vSAN data store.
The cluster initialization process performs an inventory of the disk drives on the nodes, and uses that discovery process to identify the number of disk groups on each node to be used as the foundation for the vSAN data store. The high-endurance SSD drives discovered on each node serve as a cache for virtual machine I-O operations in each disk group, while the high-capacity drives discovered are the primary permanent storage resource for the virtual machines for each disk group. The vSAN build process partners the discovered cache drives with one or more capacity drives to form disk groups, with the resulting vSAN data store consisting of this collection of disk groups.
VxRail clusters with vSAN datastores based on the Original vSAN Architecture support solid-state and NVMe drives for both cache and capacity, and solid-state and hard drives for capacity only. This architecture supports network speeds of 10 GbE, 25 GbE, and 100 GbE.