The Space in GB chart displays space utilization data counters for virtual machines.
This chart is located in the Storage view of the virtual machine Performance tab.
Total amount of logical datastore space provisioned by an administrator for the virtual machine. It is the storage size up to which the virtual machine files on datastores can grow. This includes log files, VMX files, and other miscellaneous files. Allocated space is not always in use.
Amount of physical datastore space in use by the virtual machine files.
Amount of datastore space that belongs only to this virtual machine and is not shared with other virtual machines. Only unshared space is guaranteed to be reclaimed for the virtual machine if, for example, it is moved to a different datastore and then back again. The value is an aggregate of all unshared space for the virtual machine, across all datastores.
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. If possible, you can provision more space to the datastore, or you can add disks to the datastore or use shared datastores.
If snapshot files are consuming high 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 Client user interface. For information about consolidating the data center, see the vSphere documentation.