Transaction log is a technology that provides fault tolerance and crash recovery for critical database files. Transaction logs are used in products such as the Microsoft Exchange Server directory services database and information store and Microsoft SQL Server.
Using Exchange Server as an example, data is written to transaction log files before it is applied to the directory or information store databases. This improves the performance of write operations to the Exchange databases. Transaction logs also play an important role in providing fault tolerance and recoverability for databases. If a system crash corrupts the database files, you can use the transaction logs (if they are intact) to restore all changes to the database since the last backup. Transaction logs make online incremental and differential backups possible. Without transaction logs, you would be able to perform full backups only when backing up databases online.
In Exchange, you might have several transaction logs in your database directory. When a database is backed up, the transaction logs are then purged.
Use the Microsoft Exchange Performance Optimizer tool to make sure that transaction logs are located on a stripe set for maximum performance.