Backing up the transaction log

Transaction logs can be backed up in SQL Server 2000 or later versions. Also, databases must be set in either full or bulk-logged mode. By default a transaction log is truncated after it has been backed up. However, it is not truncated following a full database or differential backup.

The main factors in deciding how frequently to back up a transaction log would be the following:

Conservation of log space.
How close to the failure point you must be able to recover in case of a disk crash.

During peak periods in a high transaction environment, it may not be unusual to back up the transaction log on an hourly basis.