Ensuring Database Recoverability

Back up the master database each time you create a new database. This makes recovery easier and safer if master is damaged.

Note: If you create a database and fail to back up master, you may be able to recover the changes with disk reinit.

The with override clause allows you to mix log and data segments on a single device. However, for full recoverability, the device or devices specified in log on should be different from the physical device that stores the data. In the event of a hard-disk failure, you can recover the database from database dumps and transaction logs.

You can create a small database on a single device that is used to store both the transaction log and the data, but you must rely on the dump database command for backups.

The size of the device required for the transaction log varies according to the amount of update activity and the frequency of transaction log dumps. As a rule of thumb, allocate to the log device 10 – 25 percent of the space you allocate to the database itself. It is best to start small, since space allocated to a transaction log device cannot be reclaimed and cannot be used for storing data.