Issue
When you log into the Delphix Engine Administration UI and go to Resources > Capacity, the amount reported for Total Capacity is smaller than the amount shown for the DATA storage section in the Delphix Engine System Setup UI.
For example:

The 46.25GB shown above is less than the 48.0GB shown below for the same storage pool.

Reason
The Delphix File System requires approximately 3% of the storage pool to function efficiently. This space is withheld from the total usable capacity. On systems with more storage, 3% can become a noticeable amount of storage. A Delphix Engine with 30TB of storage provided for the DATA storage section will withhold nearly 1TB. This is normal and should be considered when making your storage forecast calculations.