VMware vSAN is a distributed layer of software that runs natively as a part of the ESXi hypervisor. vSAN aggregates local or direct-attached capacity devices of a host cluster and creates a single storage pool shared across all hosts in the vSAN cluster. vSAN is implemented directly in the ESXi hypervisor.
Hybrid or All-Flash
We can configure vSAN to work as either a hybrid or all-flash cluster. In hybrid clusters, flash devices are used for the cache layer and magnetic disks are used for the storage capacity layer. In all-flash clusters, flash devices are used for both cache and capacity.
A disk group is a unit of physical storage capacity on a host and a group of physical devices that provide performance and capacity to the vSAN cluster. Each disk group must have one flash cache device and one or multiple capacity devices. A single caching device must be dedicated to a single disk group.
Consumed capacity is the amount of physical capacity consumed by one or more virtual machines at any point. Many factors determine consumed capacity, including the consumed size of your VMDKs, and so on.
vSAN stores and manages data in the form of flexible data containers called objects. For example, every VMDK is an object, as is every snapshot. When you provision a virtual machine on a vSAN datastore, vSAN creates a set of objects comprised of multiple components for each virtual disk.
After you enable vSAN on a cluster, a single vSAN datastore is created. It appears as another type of datastore in the list of datastores that might be available.
Specific characteristics of vSAN datastore
vSAN provides a single vSAN datastore accessible to all hosts in the cluster. Each host can also mount any other datastores, including Virtual Volumes, VMFS, or NFS.
You can use Storage vMotion to move virtual machines between vSAN datastores, NFS datastores, and VMFS datastores.
Only magnetic disks and flash devices used for capacity can contribute to the datastore capacity. The devices used for the flash cache are not counted as part of the datastore.
vSAN Deployment Options
Standard vSAN Cluster
A standard vSAN cluster consists of a minimum of three hosts. Typically, all hosts in a standard vSAN cluster reside at the same location and are connected on the same Layer 2 network.
Two-Node vSAN Cluster
Two-node vSAN clusters are often used for remote office/branch office environments. A two-node vSAN cluster consists of two hosts at the same location, connected to the same network switch, or directly connected. You can configure a two-node vSAN cluster that uses a third host as a witness, which can be located remotely from the branch office.
vSAN Stretched Cluster
A vSAN stretched cluster provides resiliency against the loss of an entire site. The hosts in a stretched cluster are distributed evenly across two sites. A vSAN witness host resides at a third site to provide the witness function. The witness also acts as a tie-breaker in scenarios where a network partition occurs between the two data sites.