If you have ever wondered why Exchange uses Transaction Logs read on.
The Transaction Logs are an important part of Exchange Server, and are used to store data before it is written to the Database. The Transaction Logs allows uses to send / receive emails, without needing to touch the database thanks to the write-ahead method of logging.
When a message is sent, the transaction is first recorded in the transaction logs. Until the transaction is committed to the Exchange database (EDB), the only existence of this data is in the system memory and the transaction logs. In the event of a crash, you lose the contents of the memory and all you are left with is the record in the transaction log. These transaction logs are crucial to the recovery of a failed Exchange server, whether it was a minor crash that required a reboot, or a more catastrophic failure requiring the deployment of your disaster recovery plans. The same goes for other transactions such as received messages, deleted items and messages moved to different folders. For this reason, it is recommended to house the transaction files on a redundant storage system, like a RAID 1 array, so that in the event of a hardware failure, no data is lost. Losing a set of transaction logs will not prevent you from restoring from your backups, but you will lose all the messages and changes since the last full backup.
