Circular logging is an Exchange feature that allows the overwriting of transaction log files. Unitrends recommends disabling circular logging. You must disable circular logging to run differential or incremental backups. If you enable circular logging, then the only type of backup that you can perform is a full.
If circular logging is disabled, the transaction logs are used to perform differential or incremental backups.
• With differential backups, these transaction logs accumulate until a successful full backup is performed.
• With incremental backups, unneeded logs are removed after each successful backup.
The removal of unneeded truncation logs is typically termed transaction log truncation. Transaction log truncation removes unneeded logs but does not reclaim space. Reclaiming space is a separate operation that must be performed periodically by the Exchange system administrator.