Presents your 
SQL SERVER E-NEWSLETTER for May 6, 2003

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CREATE A DIFFERENTIAL BACKUP

A differential backup is a backup that records only the data that has
changed since the last database backup. Differential backups are useful
because they are smaller and faster than complete backups, making it easier
to back up a database more frequently.

You use differential backups to restore your database to the point at
which the differential backup was completed. To restore to the point of
failure, however, you have to use transaction log backups.

Differential backups are preferred if only a relatively small portion of
the database has changed since the last full backup or if the same data
is modified multiple times. Differential backups are good when you're
using the Simple Recovery model, which requires more frequent backups.

You may want to use a differential backup when you're using either the
Full- or Bulk-Logged Recovery model and want to minimize the time it takes
to roll forward transaction log backups when restoring a database.

To implement a differential backup, first create a regular database
backup. Then run the differential backup periodically between full database
backups. For a busy system, this could mean running the differentials as
often as every four hours. And, if you're using either the Full- or
Bulk-Logged Recovery model, be sure to create transaction log backups even
more frequently than the differential backups.

This example creates a full and a differential database backup for the
MyNwind database.

First create a full database backup:

BACKUP DATABASE MyNwind
   TO MyNwind_1

   WITH INIT

GO

At this point, time passes until you reach the interval at which you
have decided to do your differential backup. Here we create a differential
database backup:

BACKUP DATABASE MyNwind
   TO MyNwind_1
   WITH DIFFERENTIAL
GO

In the next tip, we'll look at restoring data from a differential backup.

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