There may come a time when you must expand your cluster storage capacity since you predict more data will be added to the cluster in the near future.
Also, you are already short of space and cannot gain any more space by deleting the old snapshots and removing VM not needed any more, etc.
In that situation, assuming you have empty slots in your hardware chassis and depending on the type of the drive you are adding you will need to follow the instruction in your nutanix portal document titled “Adding a Drive”.
If you do not have any more disk slot on your hardware to, you may have to add a new node to your cluster altogether, so it can expand the capacity of your cluster. This has the benefit of adding memory and cpu resources as well.