Content are taken from various Microsoft blogs and making in sequence::
An Incremental backup of Microsoft Exchange Server 2010 database saves changes to the database that have occurred since the last Full or Incremental backup. When all the database files and log files are restored to the system, they can be recovered to the state they were in at the time of the last Incremental backup. The data stored in an Incremental backup includes only the transaction log files up to the current time.
When the backup is completed, the Exchange Server truncates the log files and marks the backup time in the database headers. Using an Incremental backup to recover a database requires the restoration of at least two data sets: the last Full backup, and then every Incremental backup taken after the last Full backup. The benefit of using Incremental backups is that the individual backups are much smaller than a Full backup and individual Incremental backups are frequently smaller than Differential backups.
The disadvantage of using Incremental backups is that if there are many Incremental backups made between Full backups, recovering the storage group may involve recovering many Incremental backups. Exchange does not allow an Incremental backup to occur when there has been no previous Full backup to establish the starting point for the incremental changes.
Since backups taken by Store Writer from the active database locations and the backups taken by Replication Writer from the DAG copy database locations both use VSS technology, these backup can be used interchangeably. A Full backup taken from a DAG copy location can be followed by an Incremental backup from the active location and vice versa. One basic restriction to keep in mind in these scenarios is the last backup state is maintained in the active database’s header, and the changes to the database header is written to transaction logs, replicated and replayed at the copy database location just like all other transaction logs in DAG deployments. Interoperability of backups and restores between Store Writer and Replication Writer enables backup applications to provide the functionality to run backups exclusively on a specific DAG node irrespective of whether the node is active or passive as well as to run backups exclusively from the passive node or exclusively from the active node.
When the VSS_BACKUP_TYPE enumeration in the Volume Shadow Copy Service is set to VSS_BT_INCREMENTAL, the following components will be included in an Incremental backup:
Similarly, if the Incremental backup is taken from the DAG copy locations using the Replication Writer, the above components will be included in the Incremental backup with the exception that in the logical file paths the \<Server Name> will be pre-pended by \Replica to designate the actual files coming from replica location.