There is not one size fits all answer for External Data Mart (EDM) size. The appropriate size for the EDM is directly linked to the sizing variables listed in How do I determine the appropriate size for my Context Store deployment?

You must also consider questions such as, how long the context data will remain in the EDM and will the data be truncated after a certain period of time.

Though the exact details might vary from vendor to vendor, the following table is a rough guide to the amount of disk space consumed by the EDM attached to a system running at high capacity with a large percentage of create and update operations.

Calculating specific quantities when the Audit Trail feature is enabled (required for Customer Journey) is a bit different as it depends entirely on the length of the audit trail stored for each context. The audit trail is the number of interactions with that context during its life span. It also depends on the amount of additional information being stored within the context object.

In an Avaya Oceana® deployment, you must include the required Avaya Oceana® service data and the additional customer created data in estimations.

For example, based on analysis of some sample data from an Avaya Oceana® lab for a voice and chat contact, the minimum context required for Avaya Oceana® (and assuming three elements created in the Customer Journey), the storage per contact is ~3 KB