One type of VxRail cluster is one where the VxRail nodes provide all the physical compute and storage resources to support application workload, and the primary storage resource is vSphere vSAN. For this cluster type, the slots in the nodes are filled with disk drives that meet the performance and capacity requirements for the application workload and are then formed into a local vSAN datastore during the cluster initialization process.
This cluster type is designed to handle most customer application workloads and covers the most common use cases.
However, this cluster type may not be a good fit for certain use cases:
Expansion of a cluster through node addition can potentially lead to stranded assets, where excess compute and storage resources cannot be shared outside of the cluster. For workloads that require a more precise balance of compute and storage resources, a dynamic cluster may be a better fit.
VxRail supports two different vSAN architectures. The first architecture is known as the “Original vSAN Architecture” and the second architecture is referred to as the “Express vSAN Architecture.”
The Original vSAN Architecture is a two-tier model built on the foundation of disk groups. A disk group consists of a single cache drive partnered with one or more capacity drives. A collection of disk groups is used to form a vSAN datastore.
The cluster initialization process performs an inventory of the disk drives on the nodes. It uses that discovery process to identify the number of disk groups on each node to be used as the foundation for the vSAN datastore. 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 datastore 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.
The Express vSAN Architecture is a single-tier model that takes advantage of the adoption of high-performant NVMe drives and the continuous increase in CPU cores to support a datastore based on a single pool of storage instead of disk groups. With this architecture, every drive can serve both cache and capacity requirements.
During the inventory process, VxRail queries the drive slots and verifies whether a datastore can be built with the Express vSAN Architecture. The datastore will only be built with this architecture if all the drive slots contain compatible NVMe drives.
If this vSAN architecture option is selected, the network configured to support the datastore must be running at either 25 GbE or 100 GbE.