In an automated financial instrument brokerage system, during a first interval, data relating to option trades is stored in an old customer account database and data relating to equity trades is stored in a new customer account database. Also, customer account data is retrieved from both the old and new databases in response to activity requests. During a second interval, data relating to option trades and equity trades is stored in the new database and customer account data is retrieved from both the old and new databases in response to activity requests. After the second interval expires, the content of the old database is copied into the new database, data relating to option trades and equity trades is stored in the new database, and customer account data is retrieved from the new database in response to activity requests. The first and second intervals define a settlement period for equity trades.