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We have a 200gb+ edb file in our Exchange for a single database with approx 40 users.

A powershell script reveals that the total size for all mailboxes should be around 90gb. I'd like to recover the difference if possible.

Will an offline defrag recover this space?

Is there a way to estimate how long an offline defrag will take?

Is the creation of a second database and shifting the mailboxes over preferable? Detailed here: https://serverfault.com/a/244232/196980

Community
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jidl
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2 Answers2

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Moving the mailboxes to another mailbox database will achieve the intended result with the least impact to the user. The users will still have access to their mailboxes while the move is in process and will lose their connection for a brief moment only when the mailbox move completes and Exchange "flips" them to the new mailbox database.

joeqwerty
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  • Is a mailbox in a different database treated exactly the same as when it was in the original? E.g.: with regards to things like distribution groups and shared mailbox access. – jidl Sep 10 '14 at 15:51
  • Distribution Groups don't have mailboxes. The mailbox is a storage container. Moving it doesn't have any bearing on mailbox permissions, DG membership, etc. – joeqwerty Sep 10 '14 at 16:06
  • Great. So given that I'm likely to schedule the moves overnight, are there any downsides to this method? – jidl Sep 10 '14 at 16:10
  • I don't see any. – joeqwerty Sep 10 '14 at 16:18
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If you have the space, creating the second database is the way I've gone in the past, but this type of task really depends on how much downtime your users are willing to agree to, or put up with.

In most cases, defragmenting the mailbox database will usually shrink the database to the reported mail size (when measuring size with the database online), plus about ~15 to 20%. However, this depends on the version of Exchange server, as versions earlier than 2013 tend to underreport sizes, as most measurements include only mail data, not metadata, or indexes. http://technet.microsoft.com/en-us/library/jj150489%28v=exchg.150%29.aspx#Mailbox

Unfortunately, defragmenting mailbox databases is usually a guesswork timeframe, the only way I've ever been able to make reasonable estimates as to how long it takes it to perform the defrag on a smaller mailbox database (usually for IT, or people prepared to go without email for a bit), then extrapolate it out and prepare for up to 10-15% extra time.

If you have another mailbox database server, creating a mailbox database copy will essentially do what you are asking too. Once the copy has been created, you can then make the copy active and remove the old, fragmented database. There's a bit more explanation on this feature on TechNet. - http://technet.microsoft.com/en-us/magazine/jj839716.aspx

Dave Green
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