Microsoft KB Archive/305519

= OL2002: Why .pst Files Are Unsupported Over a LAN or WAN Link =

PSS ID Number: 305519

Article Last Modified on 11/20/2003

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The information in this article applies to:


 * Microsoft Outlook 2002

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This article was previously published under Q305519





SUMMARY
This article tells you why personal folder files (.pst files) are unsupported over a local area network (LAN) or wide area network (WAN) link. The .pst files are not meant to be a long-term, continuous-use method of storing messages in an enterprise environment.

The article also suggests two alternatives to .pst files. You can use .ost files or Microsoft Windows Terminal Services.



MORE INFORMATION
The Microsoft Exchange Server 4.0 team created .pst files with the intent of letting a person maintain a copy of their messages on their local computer. The .pst files also serve the purpose of a message store for users who do not have access to a Microsoft Exchange Server computer (for example, Microsoft Outlook Internet Mail Only (IMO) mode users).

However, .pst files are not meant to be an enterprise network solution. Although it is possible to specify a network directory or a Universal Naming Convention (UNC) path as a storage location for a .pst file, network usage is not meant to be a long-term, continuous-use method of storing messages in an enterprise environment.

.pst files are a file-access-driven method of message storage. File-access-driven means that the computer uses special file access commands that the operating system provides to read and write data to the file.

This is not efficient on WAN or LAN links because WAN/LAN links use network-access-driven methods, commands the operating system provides to send data to or receive from another networked computer. If there is a remote .pst (over a network link), Microsoft Outlook tries to use the file commands to read from the file or write to the file, but the operating system then has to send those commands over the network because the file is not on the local computer. This creates a great deal of overhead and increases the time it takes to read and write to the file. Is addition, the use a .pst file over a network connection may result in a corrupted .pst file if the connection degrades or fails.

Other Behaviors of .pst Files over WAN/LAN Links
 * All operations take longer.
 * Write operations can take approximately four times longer than read operations.
 * Outlook has slower performance than the Exchange Client.

Recommendations
Microsoft recommends the following solutions, instead of .pst files over a LAN or WAN.

Exchange Server with .ost File
When you are working over a WAN or LAN, it is better to use the offline folder files (.ost files) to allow the remote client to work without being connected to the server. .ost files support local replication, which means that all folders and their data can be replicated to the .ost, not just e-mail messages, as is the case when you use remote mail. The use of .ost files is therefore more efficient and more useful. .ost files also do not have a dependency on the availability of the Exchange Server computer (except to synchronize new data from the server to the client and vice versa), because the information is cached in the local .ost file. This improves performance because the information being viewed is stored on the local drive while the master copy of the data remains on the server, where it can be accessed and backed up. .ost files also provide data redundancy, which ensures greater integrity and recoverability of the data.

Microsoft Terminal Services
If an enterprise wants to use Outlook over WAN or LAN links, it is even more efficient to run the Microsoft Windows Terminal Server service, either on Windows NT 4.0 or better yet, on Windows 2000 Server, than it is to use an .ost file. There are some licensing issues, but for the productivity and efficiency in preserving users' time and network bandwidth, purchasing licenses is definitely worth it. With Terminal Services, only enough information required to update a display is transferred. The cost reduction to the organization (and the potential benefit) in having many remote users based on Terminal Services rather than either .pst files or .ost files would be substantial in any network bandwidth conservation cost analysis. For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

208480 OL2000: (CW) Purpose and Capacity of Outlook Storage Facilities

177446 How to Test Microsoft Remote Procedure Call Performance

Keywords: kbinfo KB305519

Technology: kbOutlook2002 kbOutlook2002Search kbOutlookSearch kbZNotKeyword3

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