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Dealing with dwindling disk space

Three options for dealing with .PST file storage, reclaiming Exchange disk space and managing long-term e-mail archival.

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An administrator wrote me recently about a common Exchange problem: dwindling disk space. To deal with the issue, he implemented quotas to limit each user to 100 MB of mailbox space. At first, the administrator thought his problem was solved, because he got much of his disk space back. However, he soon realized that many users were getting around their mailbox quotas by storing old messages as .PST files on the file servers instead of deleting them.

While moving messages to a .PST file and storing that file on a different server does reduce the size of the Exchange information store, .PST files cause more problems than they solve. PST files are notoriously unstable, insecure, and they take up more space than if messages are just left on Exchange.

So what are your options for long-term mail archival? There are three main approaches you can use:

  1. Put disk quotas on the server where users are saving .PST files.

    By doing so, you aren't actually stopping the users from creating .PST files, but you are preventing those files from growing too large.

    Although this solution will work, the technique is a little outdated, in my opinion. I have worked for companies in the past where official corporate policy was to allow users a certain amount of disk space -- and if they needed more, tough luck. This type of policy was put into place because of limited hard disk space, and because adding more disk space to the server was expensive.

    Although the policy saved companies money, users were often forced to delete files that eventually might be needed, just to make room for new files. In an age where 200+ GB hard disks are the norm, and federal regulations such as Sarbanes-Oxley require many companies to retain e-mail indefinitely, this approach just doesn't make sense anymore.

  2. Upgrade your Exchange server to Exchange 2003 Enterprise Edition.

    This is the only version of Exchange that doesn't impose a physical restriction on the size of the information store. All other versions impose a 16 GB limit. If you have a lot of disk space to spare, but are approaching Exchange's 16 GB information store limit, this is probably the best technique to use.

    But even though Exchange 2003 Enterprise Edition doesn't limit the size of the information store, there are still some limits. You are still restrained by the server's free memory, disk space and processing power. You are also limited by the amount of data that you can comfortably back up each night. Although there is technically no restriction to information store size, current technology imposes a practical limit of just under 40 GB.

    If an upgrade to Exchange Server 2003 Enterprise Edition is beyond your budget, you may be able to get the same basic effect by creating multiple information stores on your existing Exchange server. Exchange 2003 supports up to four storage groups with up to five information stores in each group. Each information store has a 16 GB limit, but you can get around this limit by creating multiple stores.

    Keep in mind though that splitting your mailboxes and public folders into multiple information stores increases the Exchange organization's overall complexity and creates additional administrative burden.

  3. Implement an Exchange archiving solution.

    There are many different products on the market whose sole purpose is to archive old messages for long-term retention. Typically, such solutions work by storing old messages within a SQL database on a separate server. Prior to adding messages to the SQL database, the messages are compressed to save space. The archiving software works as an intermediary between the Exchange information store and the archives. This software adds messages to the database as needed and retrieves archived messages any time they're requested. Typically, the end user doesn't even know that messages have been archived because the process is transparent.

As you can see, there are several different ways you can deal with the problem of your Exchange server being low on space. No one technique is clearly superior in every situation though. You will have to determine which technique is best for your company based on your security policy, message retention policy and budget.

About the author: Brien M. Posey, MCSE, is a Microsoft Most Valuable Professional for his work with Windows 2000 Server and IIS. Brien has served as CIO for a nationwide chain of hospitals and was once in charge of IT security for Fort Knox. As a freelance technical writer, he has written for Microsoft, CNET, ZDNet, TechTarget, MSD2D, Relevant Technologies and other technology companies. You can visit Brien's personal Web site at

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