Even though disabled by default on every storage group in Exchange 2007, you may want to enable circular logging for those storage groups where you want the Extensible Storage Engine (ESE) to purge (or truncate) a log file as soon as all its transactions have been known to be committed to the database file. By enabling circular logging you don't need to rely on Exchange-aware backups to free disk space by removing un-needed log files. But can you enable circular logging on a storage group that is taking part in any flavor of continuous replication? The answer is yes, and it's also referred to as Continuous Replication Circular Logging since it is not the Microsoft Exchange Information Store service anymore who is responsible for managing circular, but it's a task handed over to the Microsoft Exchange Replication service.