The Space in GB chart displays space usage data counters for datastores.
This chart is located in the Space view of the datastore Performance tab.
Amount of physical space provisioned by an administrator for the datastore. It is the storage size up to which files on the datastore can grow. Allocated space is not always in use.
Amount of physical datastore space in use.
Maximum capacity of the datastore.
capacity = virtual machine file space + non-virtual machine file space + free space
Note: Storage data is collected and updated in the overview charts every 30 minutes. Therefore, if you refresh the datastore, the capacity value might only be updated in the datastore Summary tab, and not in the overview charts.
The datastore is at full capacity when the used space is equal to the capacity. Allocated space can be larger than datastore capacity, for example, when you have snapshots and thin-provisioned disks. You can provision more space to the datastore if possible, or you can add disks to the datastore or use shared datastores.
If snapshot files are consuming a lot of datastore space, consider consolidating them to the virtual disk when they are no longer needed. Consolidating the snapshots deletes the redo log files and removes the snapshots from the vSphere Web Client user interface. For information about consolidating the data center, see the vSphere documentation.