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Mailbox Database Size/White Space Reduction in a DAG RRS feed

  • Question

  • I have several large databases in which I'm moving mailboxes off of in an attempt to prevent my LUNs from running out of disk space. As well, I have several mailboxes of users who have left the company. My questions are as follows:

    1. When I run remove-mailbox -id "some mailbox" -permanent $true, the mailbox is deleted from Exchange relatively instantly. Will Exchange recoup the white space that is left behind after the mailbox has been deleted so that the database shrinks in size? Or will it just start writing over the white space rather than growing the size of the database?

    2. Perataining to mailboxes that have been moved, if "Keep Deleted Mailboxes for" is set to 4 days on the database that holds mailboxes that I'm moving off, will the database hold onto the mailbox (even though it has successfully been moved to another database) for the duration of the "Keep Deleted Mailboxes for" setting? Or will the mailbox be hard deleted after the move completes successfully?

    3. As part of Online Maintenance, will Exchange defrag a databse and decrease the white space, thereby shrinking the database size or will I have to take it offline to do that?

    4. What are the procedures to perform an Offline Defrag of an Exchange Databse? How risky is this?

    Thursday, January 30, 2014 11:52 PM

Answers

  • Hello,

    To answer your questions:

    1.   When and online database defrag completes a pass on the database it will reclaim this as whitespace in the database. It will not however reclaim space on the disk by shrinking the .edb file. An offline defrag is required for that.

    2.   Moved mailbox will not be hard deleted until the 4 day retention period has past, unless you manually purge them using Remove-StoreMailbox.

    3.   Related to the answer for number 1. Exchange will fill whitespace as mailboxes grow, but it will not reclaim disk space.

    4.   In a DAG you will you need to dismount the mailbox database and run eseutil /d against the active database copy. This is a relatively low risk procedure, but requires databases to be offline thus interrupting mailbox access. It can also take quite along time depending on the database size. The rate of defrag estimated by MS is 9 GB/hr. Here is a reference: http://support.microsoft.com/kb/192185/en-us

    For these types of situations my preference (If disk space allows) is to move all mailboxes to a fresh database then delete the database with excessive white space


    • Edited by Sean Greenlee Friday, January 31, 2014 2:03 AM
    • Proposed as answer by Christopher Ream Friday, January 31, 2014 2:42 AM
    • Marked as answer by ARay2014 Friday, February 7, 2014 9:49 PM
    Friday, January 31, 2014 1:54 AM

All replies

  • Hello,

    To answer your questions:

    1.   When and online database defrag completes a pass on the database it will reclaim this as whitespace in the database. It will not however reclaim space on the disk by shrinking the .edb file. An offline defrag is required for that.

    2.   Moved mailbox will not be hard deleted until the 4 day retention period has past, unless you manually purge them using Remove-StoreMailbox.

    3.   Related to the answer for number 1. Exchange will fill whitespace as mailboxes grow, but it will not reclaim disk space.

    4.   In a DAG you will you need to dismount the mailbox database and run eseutil /d against the active database copy. This is a relatively low risk procedure, but requires databases to be offline thus interrupting mailbox access. It can also take quite along time depending on the database size. The rate of defrag estimated by MS is 9 GB/hr. Here is a reference: http://support.microsoft.com/kb/192185/en-us

    For these types of situations my preference (If disk space allows) is to move all mailboxes to a fresh database then delete the database with excessive white space


    • Edited by Sean Greenlee Friday, January 31, 2014 2:03 AM
    • Proposed as answer by Christopher Ream Friday, January 31, 2014 2:42 AM
    • Marked as answer by ARay2014 Friday, February 7, 2014 9:49 PM
    Friday, January 31, 2014 1:54 AM
  • I agree with Sean.  In general, it's a better idea to make a new database and move mailboxes over.  Some of the benefits are:

    1) You'll not have to run through the risky procedure of doing a defrag.  It's a low risk procedure, but the bigger the database, the riskier it becomes.
    2) If you do mailbox moves, you don't have downtime.  2010 does online moves so you can accomplish this during normal business hours / around the clock.

    Is it possible for you to grown the volume/LUN that your DBs are on now?  Can you build a new set of MB servers and load balance?  How is your performance?

    - If you find my post to be helpful, please mark it appropriately.  Thank you.


    Chris Ream

    Friday, January 31, 2014 2:47 AM