Datastore scan collection
By default, Inventory collection only captures information about the files referenced by a collected virtual machine (VM files), and only using the information available without directly contacting the datastore. Examples of large files that will not be collected during the default Inventory collection are .iso files (such as, DVD images) and disk images (.vmdk) that are not attached to any collected VM. Data collection runtime is reduced when using the default Inventory collection, but only files for VMs in the inventory are collected. Therefore, a considerable amount of consumed space in the datastore may not be captured. Choose the option to gain visibility into the storage that is not associated with a VM.
When you check , a more detailed collection is performed by scanning the datastore to discover files resident on the datastore, but not associated with a VM in the inventory. This option, although it may impact performance, finds files that may be invisible to VMware, but that are consuming space on the datastore. For example, a VM may have been removed without deleting files from the datastore. Similarly, log files or user-stored files may be taking up space not apparent from the VM inventory's perspective.
See Reports impacted by Datastore Collection.
Note:
If an error occurs during the Datastore Scan, then only the files available with the default Inventory collection will be collected for the Datastore. It is also possible that individual files may be found via the Inventory collection, but not via the Datastore Scan.