This tip, excerpted from InformIT.com, offers advice on defragmenting the information store on Exchange Server...
as a way to free up disk space.
Exchange's online defragmentation of the Information Store only marks pages of the database as free for subsequent use by Exchange--it does not actually release the disk space. Therefore, you can often benefit by periodically using ESEUTIL or EDBUTIL to perform an offline defragmentation, which frees space for use by other applications.
Exchange 5.5 is much better about not wasting space in the Information Store than versions 4.0 or 5.0 were, an improvement that minimizes the need to do regular offline defragmentations. You will probably still want to do offline defragmentations in version 5.5 if you have recently moved or deleted a lot of data from the Information Stores, or if you are becoming concerned about the amount of disk space you have available. If you are running version 5.5 using the single-server edition, you are still limited to 16GB database sizes. If you are creeping up on that limit you may want to run ESEUTIL to buy yourself a little more time to address the problem.
Service Pack 1 for Exchange 5.5 has a handy new feature that records events in your application log to tell you how much disk space you can recover by performing an offline defragmentation of your Information Store. After you apply the service pack, each night an informational event will be recorded in the application event log's General category that reads as follows: "The database has XX megabytes of free space after online defragmentation has terminated." This information can help you determine whether you can benefit from an offline defragmentation.
The event this new feature records is particularly helpful in environments that don't enforce storage limits. I find that quite often in environments in which storage limits are not enforced, users are asked to clean out their mailboxes only when the administrator is already having disk space problems. This frequently leads to considerable disk space becoming available, which you probably wish to have released for use by programs other than Exchange. You must perform an offline defragmentation in order to reclaim the space, and because offline defragmentation requires free space available equivalent to the current size of the database being defragmented, this can become a real problem. You can help yourself out by checking the Event Viewer for storage information events and acting upon them as soon as possible.
To read more of this tip, click over to InformIT.com. You have to register to see the content of the site, but registration is free.