Let me run you through the components involved in Log Shipping with the help of Microsoft Exchange Replication Service…..!
The copier is responsible for copying the log files from the source to destination. This is an a-synchronization operation, the replication service continuously monitor the source. As soon as new log file is generated in the source, the copier will copy the log file to the inspector location in the destination.
The inspector is responsible for verifying that the log files are valid, it checks the destination inspector directory on a regular basis as and when new file is available it will check the log file to make sure that it is valid (checksum) and then copy the log file to the database subdirectory. If a log file is corrupt it will request to recopy the file.
The LogReplayer is responsible for replaying the log files in the replica database. It will batch multiple logs in a single batch replay. In LCR case the replay is performed on the local machine while in a CCR case the replay is performed by the passive node. This means that the performance impact of Replay is higher on the LCR as compare to the CCR.
The Truncate Deletor is responsible for deleting the log files that are successfully played in the target database. This is especially important after an online backup is performed at the source since a online backup delete the log files that are already played in the source database. The truncate deleter makes sure that any log files that is not replicated to the destination is not deleted by the online backup on the source.
The seeder is responsible to create the baseline content of a storage group used to start replay processing. The replication service performs automatic seeding for any new storage group.
The incremental seeder is responsible to make sure that the source and destination database are not conflicting after a database restore on the destination or after a failover in the CCR.