how does database defragmention works. when it isaid it reduces the white space so what exactly does it do? when the databsse is reduced/compressed, does it do it on the same databse or create a new one?

On Fri, 16 Sep 2011 19:30:00 +0000, Viministrator wrote: >how does database defragmention works. when it isaid it reduces the white space so what exactly does it do? It builds a new database and populates it with the contents of the old one. Then it overwrites the old database with the new one and removes the one it built. >when the databsse is reduced/compressed, does it do it on the same databse or create a new one? It creates a temporary database that will overwrite the existing one. --- Rich Matheisen MCSE+I, Exchange MVP --- Rich Matheisen MCSE+I, Exchange MVP

the database which is being built is visible?

On Fri, 16 Sep 2011 21:29:02 +0000, Viministrator wrote: >the database which is being built is visible? I guess that depends on how hard you look! Why do you want to see it? --- Rich Matheisen MCSE+I, Exchange MVP --- Rich Matheisen MCSE+I, Exchange MVP

I want to understand the architecture.

Defragmentation ... In Exchange 2010 Defragmentation works in following way, Online maintenance .. Always .. it deletes the the deleted mails and creates the white space. White space is like empty spaces created whcih are filled with new mesages. It does not decrease the size. Offline maintenance -This decreases the size of the DB, It copies each and every page to the new database and populates it.the size of the db gets shrinked as white space is deleted. The new db signature is created rendering old logs useless. and after whole process the OLD database is deleted. The procedure is OFFLINE.so you may need to Dismount the server

I want to understand the architecture. Not sure what you mean by architecture, Rich's explanation is pretty much it. For something official I guess: http://support.microsoft.com/kb/328804

Rich ans Khoj thanks both of you.

Online Defragmentation, part of background maintenance, actually moves pages around inside the existing database. Offline defragmentation (which you should never do unless there is no alternative and you are directed to by PSS) actually creates a new database. Among other things, because it's a new database the sig changes and all your old backups are now invalidated.

Just curious to know - how do you know that sig changes ? have you tried it and backup the database?

http://blogs.technet.com/b/exchange/archive/2004/07/08/177574.aspx You can backup the database. In fact, the very first thing you should do after having done something so foolish as to run an offline defrag is to take a backup. What you can't do is restore a backup from before the time of offline defragmentation and play the logs forward to current (it'll fail because the signature doesn't match the logs). It's been that way with Exchange since, well since the beginning of time... J