Transaction logs are extremely important in the running of Exchange and crucial to the proper operation. Many Admin users know about them but rarely mix it with the logs until its too late. Im going to give you an overview of the logs so you will have a better understanding for when the brown stuff hits the fan…
Exchange was built to write all transactions to these logs and then commit the changes to the database when the system allows. This way messages can be sent and received without direct contact with the database all because of this write-ahead method of logging.
They work like this…
When a message is sent the transaction is recorded in the transaction logs. Not until this transaction is commited to the database does it move from system memory so in the event of a crash, you lose the contents from memory but gain the record in the log. These transaction logs are CRITICAL to the recovery of a crashed Exchange server. The same applies for other transactions such as received messages, moved messages and deleted messages. Thats why Microsoft recommend storing the logs on redundant storage like RAID. By the way, losing a set of tran logs wont prevent you from restoring from tape, but you will lose all the messages and changes since that last full back up.
Maintain Your Logs
- Make sure you perform regular backups to commit the transactions and flush the logs.
- Make sure you place them on a dedicated drive thats set up to support heavy write loads.
- Place them on redundant arrays. RAID 1 great and RAID 5 good but not as write friendly.
- Also make sure there is plently of room on the drive, if the drive runs out of space Exchange will stop.
- Dont use circular logging unless you have very few and I mean VERY few mail boxes.