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