Sometimes replication services supplied by the data vendors will suffice. Many companies have effectively moved mainframe systems onto relational database systems such as Sybase and Oracle. For very high-volume systems, you might consider parallel processing. The leading database vendors are just beginning to demonstrate the potential of distributing database operations over loosely coupled clusters of machines. So, if your transaction loads cannot yet be handled by the vendors you are currently using, you can reasonably expect high performance increases from the next major product releases.
Disaster recovery is of utmost importance with operational databases.
With large databases in a complex environment, full reloads from tape will take too long. Some companies set up a hot standby on an alternate site, and use database replication mechanisms to propagate changes to this site continuously. If disaster strikes, the alternate machine assumes the production load while the broken system is fixed and restored. By definition, data warehouses are not operational, and therefore a long recovery will at worst inconvenience users. Your business analysts will increase in value as you seek to understand existing systems and create new ones.