A virtual datastore represents a storage container in vCenter Server and the vSphere Web Client.
After vCenter Server discovers storage containers exported by storage systems, you must mount them to be able to use them. You use the datastore creation wizard in the vSphere Web Client to map a storage container to a virtual datastore. The virtual datastore that you create corresponds directly to the specific storage container and becomes the container's representation in vCenter Server and the vSphere Web Client.
From a vSphere administrator prospective, the virtual datastore is similar to any other datastore and is used to hold virtual machines. Like other datastores, the virtual datastore can be browsed and lists virtual volumes by virtual machine name. Like traditional datastores, the virtual datastore supports unmounting and mounting. However, such operations as upgrade and resize are not applicable to the virtual datastore. The virtual datastore capacity is configurable by the storage administrator outside of vSphere.
You can use virtual datastores with traditional VMFS and NFS datastores and with Virtual SAN.
The size of a virtual volume must be a multiple of 1 MB, with a minimum size of 1 MB. As a result, all virtual disks that you provision on a virtual datastore or migrate from any datastore other than the virtual datastore should be an even multiple of 1 MB in size. If the virtual disk you migrate to the virtual datastore is not an even multiple of 1 MB, extend the disk manually to the nearest even multiple of 1 MB.