Oracle Database Backup

Curtis Preston

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Trying to back up today's databases is like trying to catch a charging rhino with a butterfly net. Real world databases have become screaming behemoths that are very difficult to capture (back up), and standard UNIX utilities are like butterfly nets. If you try to use these utilities for the job, not only will you not capture the data -- you'll break your arm! This article is my attempt to build a better rhino trap. It uses many advanced shell scripting features, so you may find it useful even if you do not have Oracle.

Hot or Cold Backups?

One of the first decisions a database administrator must make is whether to perform "cold" or "hot" backups. A cold backup involves:

1. Shutting down the instance 2. Backing up its filesystems or raw devices 3. Starting up the instance

Here are the steps to perform a hot backup. (Note that a hot backup requires much more knowledge of Oracle's internal structure, so a basic definition of helpful terms is given in the sidebar "Definitions.") First, you must determine the name of each tablespace in the instance and the files that are within it. Then, for each tablespace, you:

1. Put that tablespace in backup mode; 2. Backup that tablespace's files or raw partitions (using cp, tar, dd, etc.); 3. Take that tablespace out of backup mode.

Once all tablespaces are done:

1. Switch redolog files; and 2. Backup the control file.

It is much easier to perform cold backups, so why do hot backups at all? Simply stated, they increase your backup window, or the time in which you are allowed to perform backups. Because cold backups require a shutdown of the database, your users will probably allow only a very small backup window.