Instead of adding a new extent to a VMFS datastore, you can grow an existing extent using the vmkfstools -G command.

Use the following option to increase the size of a VMFS datastore after the underlying storage had its capacity increased.

-G --growfs device device

This option grows an existing VMFS datastore or its extent. For example,

vmkfstools --growfs /vmfs/devices/disks/disk_ID:1 /vmfs/devices/disks/disk_ID:1