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How and when to manipulate Exchange transaction logs in disaster recovery
Article ID: 812592 - View products that this article applies to.
This article describes the modification of transaction logs during disaster recovery of Exchange servers. This process is generally known as renaming of logs.
Soft recoverySoft recovery is a process that occurs if an Exchange information store that stopped abnormally is brought online. When the store stops abnormally, the checkpoint file tracks which transaction log must first be replayed to return the database to consistency. Note that soft recovery requires that EDB/E00.log, the highest log, is present.
Hard recoveryHard recovery is a process that occurs when you apply transaction logs and database patch files before Exchange 2000 Service Pack 2 (SP2), to a database that has been restored from an online backup. Note that hard recovery does not require that EDB/E00.log, the highest log, is present.
Example troubleshooting scenarioYou are troubleshooting an Exchange Server 5.5 or Exchange 2000 Server computer. The Information Store service terminated and there are 10 logs files on the hard disk. These log files range from E0000010.log to E0000019.log, and end with E00.log. You restart the Information Store service. The Extensible Storage Engine (ESE) then starts replaying the log files, but reports that the E0000015.log file is damaged. You try renaming the E0000014.log file to E00.log, and then try to mount the store again. This does not work. This is designed to fail because damaged information from the E0000015.log file may have already been committed to the database.
Example troubleshooting scenarioContinuing the troubleshooting scenario that was previously described, the E0000015.log log file has been damaged. Because of this, the E0000015.log file and all later logs cannot be reused, including the E00.log file. To make the largest recovery possible, remove all the logs from E0000015.log to E00.log. Known good logs E0000010.log to E0000014.log will remain on the disk. Then remove the checkpoint file. After you remove the checkpoint file, restore the online backup of the database. This restores the database and any log files that were included on the media backup. The log files that are restored will all be "older" than the E0000010.log file. When you have completed the restoration, the Hard recovery runs. The Hard recovery plays through the logs that were restored from tape, and then continues playing through logs that resided on the disk, E0000010.log through E0000014.log. After the logs have been played through, the database is mounted.
Note No log file renaming was required. Hard recovery does not require that the E00.log file be replayed to successfully complete.
Example troubleshooting scenarioYou are troubleshooting an Exchange 2000 Server computer. Logs E00000A1.log through E00000A7.log and log E00.log are all on the disk. The Exchange server crashes, and your database is damaged during the crash. When you investigate, you notice that the E00.log is also damaged. You have an offline backup of the database from yesterday. When you dump the checkpoint file, you notice that the last four logs were not committed to the database before the crash. To recover from this scenario:
For additional information about related topics, click the following article numbers to view the articles in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/296788/ )Offline backup and restore procedures for Exchange
(http://support.microsoft.com/kb/296787/ )XADM: Offline backup and restore procedures for Exchange Server 4.0, 5.0, and 5.5
(http://support.microsoft.com/kb/301438/ )You cannot mount a database because there is a corrupted transaction log in Exchange 2000
(http://support.microsoft.com/kb/271987/ )Overview of Exchange database architecture and engine