Since there are a lot of variables that contribute to the volume of storage we want, we need information about each of them. Gather as many data points as possible regarding things such as: largest expected tables and indexes, row counts per day, indexes per table, desired excess, and anything else imaginable. We'll use all of it.
This is much easier if we already have a database, and are now trying to ensure it is highly-available. Even if the database is only in development or staging environments at this moment, a few activity simulations at expected user counts should provide a basis for many of our numbers. No matter the case, revisit estimates as concrete details become available.
