A Core has 2000 GB of storage allocated to the repository, but the Home tab of the UI only shows 1800 GB for the Total Size of the repository.
The Core's repository is split into 2 sections. One is for storing the individual recovery points. The other stores the recovery point indexes and metadata information. The indexes and metadata use approximately 10% of the allocated space. The Home tab only reflects the amount of storage available for recovery point storage and excludes the storage required for the index and metadata information.
To determine if this is the case, just take the total allocated size and multiply by .10 (10%). The result will be approximately the size of the difference between what's allocated and what shows on the Home tab.
Example: 2000 GB * .10 = 200 GB. 2000 GB less this 200 GB = 1800 GB
There is also an additional 5-10 GB that is reserved for Windows File System operations that does not show in the allocated storage on the UI.