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Using an external hard drive to defragment Exchange

If you don't have enough free space to perform a defragmentation, and you can't add hard drives to the server, using an external hard drive offers one possible workaround.

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Over time, Exchange databases suffer from internal fragmentation that can hinder performance. The best time to defragment them is when there have been major changes to Exchange user accounts -- an influx or exodus of users, for instance, or a major departmental reorganization. To this end, Microsoft provides the command-line tool, ESEUTIL.

The bigger the .EDB file, the harder it is for ESEUTIL to defragment it. The system requires at least as much free space as the size of the .EDB file to perform a defragmentation, much in the same way a drive needs at least a certain amount of free space to be defragmented. Microsoft's standard recommendation is 110% of the size of the database itself: if you have a 25 GB Exchange database, then you'll need about 28 GB free space to defragment it.

It's entirely possible you may find yourself in a situation where you don't have enough free space on the drives in the system to do the defrag, and you can't add hard drives to the server (perhaps because it's hosted remotely or has other services running on it that can't be taken offline).

One possible solution, if you have USB 2.0 ports on the machine, is to mount a removable USB 2.0 hard drive and use that as temporary space for ESEUTIL to perform the defragmentation. Firewire drives are also fine, although USB 2.0 is a little more prevalent (and anecdotally a little faster) than Firewire. (Don't use USB 1.1, which is far too slow to handle this kind of work.)

Two of ESEUTIL's command-line switches, the /t and /s switches, control where temporary and streaming files are kept during the defrag process. With them, you can point ESEUTIL to the temporary drive as scratch space. (Don't attempt to point ESEUTIL to a network-shared drive as scratch space, unless you want to saturate your network and slow the defrag process down to a crawl. Use local hard storage of some kind, whether a drive mounted permanently in the system or an external one.)

About the author: Serdar Yegulalp is editor of the Windows Power Users Newsletter and a regular contributor to

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