Registry Change / Database Size in Exchange 2007 Standard

Posted on 2009-12-16
Last Modified: 2012-05-08
I'm trying to figure out exactly what our database size limit in Exchange 2007 Standard is.  I know the registry has been changed to provide more space.  Currently, the registry looks like this:

Database Size Limit in GB = 0x000000100 (256)

Does that value mean that the database size is 256GB?  When I look at the properties of this key, the value is 100, but it is the Hexidecimal option.  

I'm wanting to monitor the database, and make sure we are not close to reaching the limit.  Currently, the C: partition has 91.7GB of free space.  When I look at the .edb file in Program Files\Microsoft\ExchangeServer\Mailbox\FirstStorageGroup, the current size of the .edb file is 91.8GB.

Thanks for any insight into this.
Question by:david_greer
    LVL 14

    Expert Comment

    yes, the limit is 256GB (decimal value) not the 100 hex value.

    However, this is also the size of DATA in teh DB, so the actual file can be larger than that as the DB will have white space in it.

    Author Comment

    Okay............I follow you on the first statement.  I understand now that the database size limit is 256GB.  That's what I was wondering about.  The main thing I was worried about was getting close to the database size limit and the store dismounting.............but from what you are telling me, we have a long way to go before that happens.

    However, you lost me on that last statement.  What do you mean by "this is also the size of DATA in the DB?"  When I check the .edb file, it currently shows 91.8GB.  

    I understand the concept of whitespace.  Let me make sure I am correct on this though.  Example.........I deleted all mail from two mailboxes today, which came to a total of about 8GB.  Am I correct in my thinking that the actual .edb database will not reduce in size (it will stay 91.8GB), but will fill in that 8GB of whitespace before the .edb database begins increasing in size again?  I know that the regular nightly online maintenance does not reduce the size of the database.  I will have to run an offline defrag using eseutil to actually reduce the size of the .edb.  But, if our database size limit is 256GB, then no need to run the offline defrag, correct?
    LVL 14

    Accepted Solution

    Every night exchange runs cleanup processes etc.

    For example, you have 100GB of data in your exchange DB. Users cleanup and delete a heap of mail, or you delete some mailboxes. The total physical database size won't shrink. But when Exchange checks the database size, it will only detect the actual used space inside the DB.

    So it is possible you can be in the situation where:
    exchange data = 95GB
    MDB file size = 110GB.
    Exchagne won't dismount the file when it goes over a 100GB limit, only when the Exchange data is over 100GB.

    Around 5am in the application event log you will see some 1221 event ids.

    If you look at it one will say something like: The database "First Storage Group\Mailbox database" has 1988 megabytes of free space after online defragmentation has terminated.

    That means there is almost 2GB of empty space in the DB. The storage limit you set in the registry is baed on ACTUAL exchange data, not physical size on disk.

    Author Comment

    Okay, I think I am beginning to follow you.  I actually just checked on our Exchange Server, and found a 1221 event at 3:59 this morning............."The database First Storage Group\Mailbox Database has 697MB of free space after online defragmentation has terminated."

    So does this mean that Exchange will "fill in" that 697MB FIRST, before it begins increasing the size of the DB?

    Overall, I guess the main thing was to make sure I wasn't close to running out of room on the database.
    LVL 14

    Expert Comment

    Yes pretty much. As long as the online maintenance is running fine each night, it will cleanup and remove delted items, allowing you Exchange to use the whitespace effectively.
    LVL 27

    Expert Comment

    By the way, never run an offline defrag in Exchange 2007, absolutely no need to.

    Just create a new mailbox database and then move the mailboxes to the new DB.

    Also, Exchange allows you to have up to 5 DB's, it might be an idea to split up some of the users into different SG and DB's as its often easier to deal with smaller DB's and not so disruptive if the DB becomes corrupt for some reason. Not all eggs in one basket.


    Author Comment

    Thanks for the added tip shauncroucher.  I appreciate it

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