Use dump database to make several practice backups of an actual user database and dump transaction to back up a transaction log. Recover the database with load database and apply successive transaction log dumps with load transaction.
Keep statistics on how long each dump and load takes and how much space it requires. The more closely you approximate real-life backup conditions, the more meaningful your predictions will be.
After you have developed and tested your backup procedures, commit them to paper. Determine a reasonable backup schedule and adhere to it. If you develop, document, and test your backup procedures ahead of time, you will be much better prepared to get your databases online if disaster strikes.
