This function allows to control storing of physical files either on SAP Server (by default) or external server.
Functional details
Once the content repository /DBME/MMA is configured with external server, all MSA pictures and attachment are stored in external server.
Migration
To migrate files from SAP server to external server you can use standard migration tool described in SAP note 389366
Technical Information
To use custom document model, you need implement BadI /DBME/MMA_BADI_DOC_MODEL