In the recipe Expanding/growing a VMFS datastore, we discussed the procedure involved in increasing the size of a datastore on the same LUN backing the VMFS volume, and that was possible only if the LUN has unused free space on it or was expanded.
You can run into a situation where there is no unused space on the LUN backing the VMFS volume, but your datastore runs out of space. Fortunately, vSphere supports the spanning of a VMFS volume onto multiple LUNs. This means you can span the VMFS volume onto a new LUN so that it can use the free space on it. This process of spanning a VMFS volume onto another LUN is called extending a VMFS datastore.
The VMs running on the volume can still remain powered on while this task is being accomplished. The following flowchart provides a very high-level overview of the procedure:
