Unix Backup and Recovery

Logical Backups

The dump command is a very powerful backup tool, but there are limitations to its abilities. For one thing, it can only back up all of the database objects together. If a backup of a single table in the system is needed, this command cannot be used. Also, the dump backups cannot be used to copy a database between servers running different operating systems; this is because the backups are copies of the data disk blocks, and these disk blocks are dependent on the operating system. The need to back up only parts of a database and make them useful on all types of operating systems is why Sybase created the logical backup utility bcp. This utility also provides the final piece to make sure all the information needed to restore the data server is collected.

bcp provides another key feature. Because it refers to the internal structure of the database, it is an excellent tool to confirm whether there is corruption, while also backing up the data. The bcp command will error out if it has any problems reading the data out of the system.

The two drawbacks to bcp are that:

• It takes much longer to use it to back up the whole database than it takes with the dump command.

• Every single object in the database would have to be backed up separately, and any stored procedures, triggers, or other nondata objects would have to be output using a different method.

The bcp command is run at the operating system level like isql, and it too takes a number of different parameters. This discussion ...