Communicate clearly how much disk space is available for databases

Other than disk space for UNIX users, which is unlimited and billed after, databases are stored on the node disk with a fixed size.

The node disk contains logs, temporary files, etc. -- of which the size is not accurately predictable beforehand, and depends largely on the customer's usage. We use 20% as a rule of thumb.

We should clearly communicate that on average, 100% - 20% = 80% of the node disk space is available for databases.