To increase the capacity (grow or extend) of a VMFS datastore successfully, ensure that the device has been increased from the backend SAN.

Once completed, initiate a cluster level rescan to ensure that the Extent Device list contains updated list and then use the Increase option.

If the device for which size is increased from backend SAN is exposed to multiple hosts in multiple clusters, then cluster level rescan has to be triggered on all the clusters where device is visible.

 

Symptoms:
When you try to grow or expand a VMFS volume by clicking the Increase option, there are no available devices to select.

VMware ESXi 4.1.x Installable
VMware vSphere ESXi 5.1
VMware vSphere ESXi 5.0
VMware vCenter Server 4.1.x
VMware vCenter Server 6.7.x
VMware vSphere ESXi 5.5
VMware vCenter Server 6.0.x
VMware vCenter Server 5.0.x
VMware ESX 4.1.x
VMware ESX 4.0.x
VMware ESXi 4.1.x Embedded
VMware vSphere ESXi 6.0
VMware vCenter Server 4.0.x
VMware ESXi 4.0.x Embedded
VMware vSphere ESXi 6.7
VMware vCenter Server 5.5.x
VMware vCenter Server 5.1.x
VMware vCenter Server 6.5.x
VMware vSphere ESXi 6.5
VMware ESXi 4.0.x Installable

To increase the capacity of the VMFS datastore:

1. Initiate a Cluster level rescan (incase the device is shared across multiple hosts/clusters) or on the host (incase of a stand-alone host) so as to force the ESXi host(s) to sync in with the change for the underlying devices expansion.

2. Right click on the cluster/host and select Storage > Rescan Storage.
   
   
    
3. Navigate to the Datastore View and select the Datastore.
4. Navigate to Configure > Device Backing and select the Extent Name.
   
   
   
   You should be able to see the Device Details reflecting the update capacity basis the expansion done from the SAN.
   
   Note: In this example, the datastore iscsi1 was configured for 250 GB and the underlying device was expanded to 400 GB. 
   
   If the underlying device is not reflecting the updated info, attempt a cluster/host level rescan once again so that the fields highlighted in the image above indicate the desired change. The following steps would need to be followed ONLY if you are able to detect an increase in the capacity of the underlying device.
    
5. Log in to one of the hosts that has access to this datastore via the GUI (host client) using the root credentials. 
6. Navigate to Storage > Datastores and select the datastore in question.
7. Right click on the datastore and select Increase Capacity. Alternatively, select the option at the top to perform the same (highlighted in green).
   
   
8. You would be prompted to select one of the two options. Add an extent to existing VMFS datastore or Expand an existing VMFS datastore extent. 
   
   Note: The first option is to create multi-extent datastores by spanning (adding) a new volume to the existing datastore and the second option is to increase the capacity for the existing device itself. In this example, proceed with the second option. 
    
9. You should be able to view the device extent as indicated in the screenshot below. Select the device instance and click Next.
   
   
    
10. Select the VMFS partition as highlighted in the image and use to side-scroller to indicate the range of the expansion that would need to be done and click Next. Once completed, click on Finish. You should now be able to view the datastore expansion having completed successfully.
     
11. Considering this expansion activity was directly on the host by bypassing the vCenter Server. VMware recommends that once the expansion is completed at the host level, a cluster level rescan is initiated so that all the hosts that have access to this datastore are in sync with the expansion that was just recently performed. 
    
    Note: If a cluster level rescan is not done from the vCenter Server level, there are good chances that the vCenter Server might not readily detect the change and there would be a disparity in the current space/usage for the datastore in question. VMware recommends that a cluster level rescan at the vCenter Server level is always followed after any form of expansion being done at the host level.  
     
12. You should be able to view the datastore reflecting the updated capacity uniformly across the vCenter Server.

VMware Skyline Health Diagnostics for vSphere - FAQ

Performing a rescan of the storage on an ESX/ESXi host
Cannot see some or all storage devices in VMware vCenter Server
Expanding Local Datastore in vSphere ESXi
Como aumentar ou expandir volume ou armazenamento de dados do VMFS
Ampliación o expansión de un volumen VMFS o un almacén de datos
无法增加或扩展 VMFS 卷或数据存储
VMFS ボリュームやデータストアを拡大または拡張できない