If I move mailboxes to another DB rather than running a defrag does that break the single instace storage?Eric

Yes.Single Instance Storage will basically pull out the data it needs when moving the mailbox to a new database. Here is a good link on what SIS is: http://msexchangeteam.com/archive/2008/02/08/448095.aspxand how it works. SF - MCITP:EMA, MCTS

SIS will not break.When items are created in the new DB, there is logic to maintain the SIS as long as it was SIS on the old DBIf you ask me, SIS is not that much of a deal since you wont save that much space as you think you do.SIS will even be removed in Exchange 2010 due the rearchitecture of Exchange databases.lasse at humandata dot se, http://anewmessagehasarrived.blogspot.com

SIS will come in to picture when you want to archive/Exmerge your Mailbox to PST. SIS will not break by moving the MB from DB to another DB. If you are worrying about DB size then put Mailbox Quota or check for event id 1221 for White space and depending on that take a call for offline Defrag. Vinod |CCNA|MCSE 2003 +Messaging|MCTS|ITIL V3|

Moving MB's to another DB is one of the easiest ways to be honest, since you can queue up a time to do the MB moves at night and not have to sit and wait for a defrag to complete then remount the DB after its done.Being we can have very little down time on our servers here in Iraq its just easier to move a mb and have a user get a prompt to close and open outlook with an MB move at night than to take down a whole db for a few hours.

Hi,Yes, Moving Mailbox breaks Single Instance Store. Please find the details description in the below linkhttp://support.microsoft.com/kb/175481regards,Krishnahttp://smtpport25.wordpress.com