If all you want is to take a backup while the database is still available it is much easier to use the "ONLINE" option of the backup command. Remember to use the "INCLUDE LOGS" option too : it doesn't become the default until V9.5 I think.
This is much easier both to set up than split mirror. You can throttle the backup so that it doesn't interfere with your online performance too.
I assume you already have set up archive logging to write logs to an off-server location automatically ?
If you have backup servers such as TSM or Veritas NetBackup at your disposal then you can write backups and logs directly to these automatically. Schedule the backups either using the built in DB2 scheduler or your scheduling tool of choice and it becomes basically "no further action required".
... just wanted to ensure you weren't putting yourself to more work than is necessary.
We do all our restores into development from TSM : we've managed to work out how to switch between our production and development TSM servers at will and probably know more about TSM than we ever wanted to know :-(
We're going to have to start looking at alternative ways of producing copy databases, since some of our production databases are now bigger than the capacity of our development servers. Optim looks like one potential solution, and also gives us added benefits in terms of data scrambling and security.