Dell EMC Unity: Cannot expand storage pool; not enough drives (customer correctable)

User added 3 drives to array.  He now has a total of 4 drives  available.  (In my customer's case; these quantities may vary depending on your customer's RAID type).

User has added new drives to Unity array and is attempting to expand storage pool.  He cannot since it says that  he does not have enough drives available.

Unity provides for two storage pool architectures; Dynamic Pools or Traditional Pools.

Dynamic Pools can be expanded with as little as one or two drives at a time.

However, to expand Traditional Pools, you must have a minimum number of drives based on the RAID type in use.
      RAID 5                5
      RAID 6                6
      RAID 1/0             2

User was using Traditional Pools and therefore did not have minimum number of drives to expand (customer in my case was using RAID 5).

To determine if customer is using Traditional or Dynamic Pools....

 1.In Unisphere, in the upper right, click on the Settings button (looks like a gear).
 2.In the Settings window, click on the Storage Configuration tab on the left.
 3.If you're using OE code 4.2, you should only have the Drives sub menu under the Storage Configuration tab.  It will list how many drives you have of each type/size and on the far right, it will show how many are configured as part of a dynamic pool and how many are configured as part of a traditional pool. 

For more info regarding Dynamic Pools vs. Traditional Pools please see Dell EMC Unity:  Dynamic Pools Overview.