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Exchange Server - A Brief History
The Miscellaneous Atom Exchange and Active Directory Support for NetMeeting Performance and Virtual Memory
Exchange Server has gone through a few changes since its arrival as version 4.0. The architecture still holds a lot of the same features but the capabilities have been through all sorts. The biggest differences immediately obvious to the eye concerning the changes to Exchange Server will undoubtedly include the new way Exchange 2000/3 runs all of its processing in memory using the miscellaneous atom so it is safe from corruption during, for instance, power loss, and also the way in which the Directory Service is accessed and stored. The miscellaneous atom is not a new idea but it was used by Microsoft in their Windows Server products in 2000 in both Exchange and SQL 2000. It basically revolves around the idea that when you are adding or changing data to a database, all of the processing is done once the log file has been loaded into physical memory and so the change to the database file, if interrupted, is entirely lost as opposed to being part-done and so leaving the database in an un-mountable state. The atom metaphor being the idea that log files enter the system in physical memory and leave again as discrete, changed or unchanged entities, indivisible just as the original Greek meaning of the word atom, meaning fundamental, indivisible particle. The outcome of this being that the database remains indirectly connected to the processing elements of the system and always decipherable by the system on start-up. The Exchange database also comes in a few parts with version 2000, as well as the additional miscellaneous atom file temp.edb, there are files for streaming media databases named *.stm files. These files exist for each public and private database respectively and handle the streaming media content. The overall EXCHSrvr directories remain pretty much the same though, including most of the same files and folders from v5.5. MDBData is still the folder for the databases themselves, mtadata for the message transfer agent which still handles all message transfer from and to the information store. Exchweb is the file system for OWA which is now almost identical to Outlook 2003 and %Servername%.log is the log file. SRSData is for the Site Replication Service which will be disabled in a single server/single site install and Conndata is connection data including Exchange Server routing tables. Bin is still where the application files are kept and OMA is for the new Mobile Outlook features for PDAs including folder browsing and mail facilities. ExchangeServer_&ServerName% in the case below, EMAIL is the virtual server directory and the schema directory contains all of the .XML files for the schema. An important consideration to bear in mind is that of Antivirus. Make sure you have a proper store scanning mail solution and with the real-time scanning system, configure it to scan only \Address, \Bin,\Exchweb, \Res and \Schema and NOTHING ELSE. If you are losing calendar items or the like it is because the antivirus system real-time protection is scanning and removing them as they are entered or held in the information store. This must be halted as it can leave your Exchange Database unmountable and unusable. In the image below you will also notice that the EXCHSRVR directory is inside of the \Program Files folder. This is a default of an Exchange 2000/3 install and will not apply to an upgrade which will be in the root of the drive by default.
Windows 2000 Active Directory was based on the X.500 system of Exchange which was in turn based on X.400 mail systems, which was made available to really only very big players in the market as the network required was a dedicated-private system that would have to be routed between each site. British Telecom supplied a lot of Government Bodies with the system early on such as NHS-Net and the like. X-400 systems can be configured to accept SMTP mail at the X.400 Gateway. The system needs to convert the address from the [email protected] to the field-based system that X.400 uses. Typically transcribed as g=given name, s=surname, i=initial etc. As Active Directory was based on the Exchange 5.5 Directory so, it too, shares attributes of X.400. Exchange was born with version 4.0 which was actually the first release and was named to try attract users of Microsoft Mail which was at version 3.5 at the time. Although Exchange was sold as version 4 to represent an upgrade, it was a full migration to a completely different system. Exchange 5.5 was the first version to include an Internet Mail Connector capable of interpreting the Simple Mail Transfer Protocol. Exchange 5.5 called all of the SMTP addresses, 'Internet Addresses' and was the first version really supporting external mail. If you have a look through Active Directory with ADSIedit you can see all of the x=this and y=that notation carried over from X.400 architecture. Now that the architecture is unified for Exchange and Windows Directory there are issues with putting Exchange 5.5 on Windows 2000 Active Directory Domain Controllers. LDAP (Lightweight Directory Application Protocol) does a lot of communication on port 389 or 636(SSL) and as both directories are based on the same system then they conflict. (See http://support.microsoft.com/default.aspx?scid=kb;EN-US;224447 on how to alter this) Exchange 2000, however uses port 379 or a user configured port number for intra and inter-site messaging and so this is no longer a problem. It is worth remembering, though, that Microsoft advise not to put Exchange on any Domain Controller and I would add that I consider this very sane advice. Exchange 2000 connects to Active Directory with an application called the Exchange Active Directory Connector which is included on the Exchange 2000 Server CD. This is different from the one included with Windows 2000 which is designed for connecting Windows 2000 to the Exchange 5.5 directory for synchronising usernames from Exchange into Active Directory (I.E. controlling Active Directory Users and Computers with Exchange Administrator.) Exchange 2000 included a lot of support for NetMeeting and Microsoft Chat which came along with Exchange Enterprise Edition and the full blown collaboration system Exchange Conferencing Server. Exchange Enterprise was a NetMeeting Directory Server as well as a Chat server and Instant Messaging server whilst Conferencing Server was a web-based extension to the system which was accessed through IE and plug-ins incorporated NetMeeting into a complete collaborative experience. The reason none of this lived until Exchange 2003 is basically down to MSN and Windows Messenger. Yahoo Messenger and AOL were freely available and Microsoft had to do something to stay with the pack and so Windows Messenger wound up being packaged with XP and has evolved into a very useful product.
Virtual memory should have been set to twice the physical memory when installing Exchange 2000/3 and if possible the Log File for each database should be allotted its own HDD or certainly its own partition. This is done so that the log file can be written incrementally and, if configured, can vastly improve Exchange Server performance. The latest and greatest developments are really those of RPC over HTTP which allow - as the name implies - Remote Procedure Call over port 80 HTTP which means that Outlook 2003 can connect to Exchange Server without opening any ports other than those for Email and OWA access. The system can be configured with a Front-End Server at the gateway which routes all requests to a server which can be placed behind another Firewall out of the DMZ. This means that your mobile users can update their mobile or laptop copy of Outlook without dialling in to the LAN and so always have a single up-to-date email information console.
Exchange Server is a large and complicated application and can be every bit as complicated as Windows 2003 when deployed into Enterprise level sites. Many of the issues tend to arise with message routing, AD connection and client connection/permission problems. Since Exchange 2000 I have found the system to be fantastically reliable, capable of being thrown in a cupboard somewhere in an enterprise and working away happily without concern as long as AD and SRS are configured suitably. The need to keep Exchange on a dedicated, member server is valid for any more than perhaps 100 users as if there is only the one server on-site, once the file sharing, Antivirus, DNS, AD, DHCP and all the rest of it are configured, the strain can be considerable but if there is only one server onsite don't worry, the system still works and works well even below the minimum memory and processor specs given by Microsoft. Watch out for funny routing issues that can begin with SRS problems and do not forget that you can always add a new Site Replication Connector if there is too much traffic or if you lose the SRS master server. Active Directory is a large and complicated system and extra functionality brings new problems but http://support.microsoft.com is a very useful tool. If you cannot find your problem there then it is an unusual one, so report it to Microsoft. I find that they are usually bringing out a hotfix pretty quickly once customers start to raise issues. If the stores keep un-mounting then check on the disk space as since 2000 they shutdown automatically to avoid corruption.
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