Exchange 2000 Server Transaction Logging
Transaction log files are used to store Exchange message changes before they are made to the database. Files in c:\program files\exchsrvr\mdbdata\Exx.log and d:\program files\exchsrvr\secondstoragegroupname\Exx.log.
Transaction Log files and backups - circular logging is off by default. When backups are done and circular logging is off, the log files are deleted. It is recommended that circular logging remain off for all except stores that generate transactions that do NOT need to be recovered..
Checkpoint files are denoted with the .chk file extension. They indicate the point at which Exchange is caught up writing the transaction log files to the database. If there is no checkpoint file, Exchange must look through every transaction log file to determine where it left off writing transactions to the database.