INF: Differential Backup Time Considerations

SUMMARY

A differential backup only records changes made to the database since the last full backup was made. While typically much faster than a full database backup, elapsed time for SQL Server 7.0 differential backup is roughly proportional to the allocated space in the database. Consequently, a differential backup on a very large database may take longer than expected, even if few changes have occurred since the last full database backup.

If the amount of time required for a differential backup is too large, you should consider doing log backups instead.