vSphere Datastore Introduction 

Datastore as logical containers or logical units for storage. This storage is used to store virtual machine… Storage, for example can be based on one or several HDD or SSD
The storage can not only provide using HDD or by Directly Attached Storage, but it can also provided by NAS or SAN, these are storages which are accessed using some network.
We need a file system which control that how the data is saved and retrieved from that storage. For example, we can have VMFS or NFS