TRANSACTION LOG FILES 137 Transaction Log Files The ESE database engine uses write-ahead logging. All transactions are first written completely to transaction logs prior to being committed to the database; this gives ESE the atomicity and durability features of an ACID database. As discussed earlier in this chapter, transaction logs are critical to the operation of Exchange Server. There will be a unique set of transaction logs for each storage group, and each set of transaction logs should be located on a separate physical hard disk. Exchange log files are always 5120KB in size; if you find a log file that is a different size (except for the Enntmp.log file), either it is not an Exchange transaction log or it is corrupted. (Windows Active Directory uses a transaction log file size of 10,240KB; these files are named slightly differently, too.) Each storage group has an assigned log file prefix. The first storage group uses E00, the second storage group uses E01, and so on. The active log file in the first storage group transaction log file directory is E00.log. When this file fills up, it is renamed to e0000001.log, and a new E00.log is created. When the newly created log file fills up, it is renamed to E0000002.log, and another new E00.log is created. If you view either of these directories, you will see a collection of these old log files. NOTE All subsequent examples use the prefix E00. If you are managing more than one storage group, you may have a log file prefix of E01, E02, or E03. When circular logging is disabled (the default), transaction logs will accumulate until a normal or incremental backup is run. On an Exchange 2003 server supporting 1,500+ active mailboxes, I have seen a single storage group generate 2,000 transaction logs in less than 48 hours. Regular backups must be run to ensure that the transaction log file disk does not run out of disk space! WARNING Never delete transaction logs manually unless instructed to do so by Microsoft Product Support Services (PSS). Don t panic if you see a few hundred megabytes or even a few gigabytes of transaction logs accumulating each day. A gigabyte of transaction logs does not mean a gigabyte of new messages; it means there have been a gigabyte of transactions against the database in that storage group. Transactions include not only the newly arrived messages but also any changes to the database (moves, folder creations, deletions, modifications, permissions changes, and so on). As I stated earlier, the transaction log files should be on their own physical hard disk. You should have sufficient disk capacity to allow a week to two weeks of transaction logs to accumulate, if necessary. WARNING Never enable disk compression on any Exchange database, transaction log, tracking log, or queue directory. This hurts performance and could cause larger database files to become corrupted. Too Many Log Files? I know what you may be saying to yourself right about now. You are probably saying Self, if the log files are named E00xxxxx.LOG and they use a hexadecimal numbering scheme, won t I eventually reach E00FFFFF.LOG? You are correct; eventually you will reach that particular log file generation name. I used to tell people this would probably not happen very often. After all, that is 1,048,575 log files, which is a lot of transactions! But in this day and age of server consolidation and cluster nodes that support 5,000

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