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Beware of the information store's outer limits

Once you reach the 16 GB limit of Exchange 2000 and 2003's information store and it shuts down, what are your options? This tip explains the alternatives and offers some advice.

Your information store in Exchange Server 2000 or 2003 reaches 16 GB, and it automatically shuts down and you can't restart it.

Hopefully you were prepared for this safety feature, which is designed to prevent you from corrupting the database by inserting more data than the database can hold. In any event, what are your alternatives?

One option is to upgrade to Exchange Server 2003 Enterprise Edition, which does not impose a 16 GB limit. Other options are creating a new information store and moving some mailboxes to it, or buying another Exchange Server and migrate some mailboxes. In either case, you must first get your existing Exchange Server back online.

If you aren't in an extreme rush to bring the server back online, I recommend first attempting an offline defragmentation of the information store. Exchange defragments the information store on a regular basis, but never actually releases any free space that may exist within the database. Running an offline defragmentation will often shrink the database enough to allow you to mount it and start moving mailboxes to an alternate location.

To perform an offline defragmentation, open a Command Prompt window and navigate to \Program Files\exchsrvr\bin. Now, enter the following command: ESEUTIL /D <database name>

You should remember two things about an offline defragmentation. First, it takes a few hours to defragment 16 GB of data. Second, you must have about 17 GB or more of free disk space on the volume containing the database because the defragmentation process must write a temporary copy of the database.

If you don't have the time or disk space to defragment the database or if the defragmentation process doesn't shrink the database enough, there is another option. You can modify the Windows registry and configure Exchange so that it allows the Exchange database to be 17 GB in size. Keep in mind that this is intended as a temporary fix, not a long-term solution. You still need to move some mailboxes and decrease the database's size. (Before I show you this little trick, you should know that editing the registry incorrectly can destroy Windows and/or your applications, so you should perform a full system backup before continuing.)

Use the REGEDT32 command to open the Registry Editor. When the Registry Editor opens, navigate to HKEY_LOCAL_MACHINESYSTEM\CurrentControlSet\Services\MSExchangeIS\server name\Private-some really long hex string.

With the Private container selected, select the New | DWORD Value commands from the Edit menu. Now, create a new DWORD called Temporary DB Size Limit Extension. The value name is case sensitive. Assign the new registry key a value of 1. Finally, close the Registry Editor and you should now be able to mount your database.


Brien M. Posey, MCSE, is a Microsoft Most Valuable Professional for his work with Windows 2000 Server and IIS. Brien has served as the 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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