Shrink Exchange Drives

kmwestergaard
kmwestergaard used Ask the Experts™
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What is the best way to recover space that is being used by my exchange mailboxes on one of our drives? Over the past few  months we have removed several mailboxes for various reasons, but have not noticed a change in the amount of space taken up when doing so. Do i manually need to run a defrag to clean up some space?

Thanks in advance,
Kristin
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Site Reliability Engineer
Most Valuable Expert 2011
Commented:

Kristin,

You're seeing a 'feature' of exactly the way Exchange's database engine was designed to operate. When data is removed from the database (which may be a while after it is actually deleted, through item / mailbox retention), the database pages that data previously occupied are marked as 'whitespace'. Rather than release that empty space back to disk, it is withheld in the database for future use as the database grows. As new data is added, the whitespace is used before extra space is allocated on disk.

You can reclaim that space by a number of methods. The common suggestion is an 'offline defrag', which involves taking the database offline (yes, downtime) while a tool copies data from an old database to a new database, then removes the old. This has inherent risks and can be slow, resulting in hours of downtime for your mail system.

The alternative (especially on Exchange 2010, where you can create multiple databases) is to create a brand-new database, move all the mailboxes to the new one, then delete the old. This process has zero risk and zero downtime for your users; it is a fully online operation.

With that said, unless the free space in the database is astronomical AND you desperately need to re-purpose that space, there is little point in carrying out these operations. The free space will eventually be used up by new data as it arrives. If you do decide to go ahead, go for the second method rather than the first, but in the vast majority of cases, there is never a compelling reason to mess around with the data in this manner.

-Matt

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Thanks for the info!

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