By default, Exchange writes 5MB transaction logs that are kept until you perform a full backup. If the database becomes corrupted, Exchange restores the last full backup then applies all the transaction logs. However, you can turn on circular logging, which instead reuses transaction logs when the 5MB is full, but this means in the event of a database loss, data could be restored only to the point of the last backup. To enable circular logging:
1. Start Exchange System Manager (ESM–Start, Programs, Microsoft Exchange, System Manager).
2. Expand Administrative Groups, Servers, then expand the server.
3. Right-click the storage group for which you want to enable circular logging and select Properties (remember transaction logs are per storage group and not per database).
4. Select the “Enable circular logging” check box and click OK, as the figure shows.
5. Click Yes to the warning.
6. Restart the Information Store by using the following command: net stop msexchangeis net start msexchangeis