Datastore in Virtual SAN
After you enable VSAN on a cluster, a single VSAN datastore is created. This datastore uses storage from every ESXi host in the VSAN cluster and contains all VM files.
OSFS (Object Store File System) enables VMFS volumes from each ESXi host to be mounted as a single datastore. Data on a VSAN datastore is stored in the form of data containers called objects, which are logical volumes that have their data distributed across the entire cluster. An object can be a vmdk file, a snapshot, or the VM home folder. For each VM on a VSAN datastore, an object is created for each of its virtual disks. A container object is also created and holds a VMFS volume and stores the virtual machine metadata files.
Although only a single VSAN datastore is created for the whole VSAN cluster, you can have multiple datastore storage policies that can be configured with different storage capabilities.