Tomas,
There's an excellent book that comes with the Oracle documentation all about backing up and restoring an Oracle database - have a look at that.
In the meantime:
There are three basic approaches to this:
1 - Cold Backup.
Turn the database off and backup all of its files to a tape drive - make sure you turn it off first (the shutdown command in svrmgrl) Easiest, safest.
2 - Warm Backup.
This uses the exp command which exports data from the database to a file or tape device. If your database is not busy you can use the consistent=yes option to safle backup a running database. Easy, safe.
3 - Hot Backup.
For this the database has to be running in Archive Log mode. Updates to the database are also archived into a set of files. These files are archived onto tape and used to restore your system if it's needed. Read the book, test it a lot (on a test database that you're also backing up using 1 or 2). Hard, safe. Mike
michael.j.lacey@ntlworld.com
Email welcome if you're in a hurry or something -- but post in tek-tips as well please, and I will post my reply here as well.