Database scalability isn't likely to be a major issue, pretty much any major database can handle the volume of data you're likely to need. Security, reliabilit

Database scalability isn't likely to be a major issue, pretty much any major database can handle the volume of data you're likely to need. Security, reliability, consistency and integrity are likely to be much more important. How will your system handle encryption and ACLs, how will it recover from partial system failures, when there's an inconsistency how will you resolve the authoritative truth, how are you going to store transaction logs (i.e. read-only media), etc ?