Since you do backup the database all the time then you should forget about /b switch.
I forgot to ask, are running Exchange 5.5. or 2K
for 2K use : eseutil
for 5.5 use : ebdutil
final command should look like this:
C:\program files\ exchsrvr\bin> eseutil /d C

rogram files\exchsrvr\mdbdata\priv.edb /i
- Use the /i switch to avoid defraging streaming files and use the same command minus /i switch to defrag the streaming files separately.
- You will need to stop the Exchange services manually for this process or else you could damage the database or defrag will not even work.
-If you haven't defrag the database before the it will take about 2 to 3 hours to go through it base on speed of your server.
A word of advise. You could go into your Exchange system manager (If it is E2K) and put a check mark where is says don't mount the database on reboot, then stop the services first and do the defrag, after reboot go back into the system manager and mount the database and reboot again. the reason I say that, if for some reason you database gets corrupted during the defrag the on reboot your server will try to mount the corrupted database and you will have a mess in your hand with all the errors, if that would be the case you could load the back up into the directory and your exchange will not even know about the defraging problem... do you see what I'm trying to say... that is not a written rule anywhere but best way to protect a mis-hap.
http://support.microsoft.com/default...192185&sd=tech
http://support.microsoft.com/default...b;EN-US;143233
cheers