Exchange 2010 - disk space getting used up despite available whitespace

We’re running low on available disk space, so I cleaned up our mailbox databases and made available up a bunch of whitespace.
That whitespace is being used up in an expected fashion, however, I am noticing that some disk space is also/still getting used up.  For example, here is one of our databases over 3 dates:

Date              DB size         Whitespace      Free disk space
July 14    --    955.7GB    --    31.19GB    --   8.75GB
July 22    --    955.7GB    --    29.13GB    --   8.41GB
July 23    --    955.7GB    --    27.44GB    --   8.35GB    

Is this normal and part of an overhead of disk space that gets used, despite having available whitespace?  
And if so, is a daily 4-6% overhead/decrease to be expected?

Note.  The drive in question is holding only that database, nothing else (logs on a different drive, OS on a different drive, etc).
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RantCanSr. Systems AdministratorCommented:
Is exchange baremetal or virtual?

The growth seems normal, and yes, there will be shrinkage despite the whitespace. I would never recommend defragging a healthy exchange DB, as indicated in this walkthrough.

If you are concerned about data growth, you can apply autoarchive policies to users mailboxes, which will create local PSTs on local or shared drives, as shown here:

If this is critical, you can add storage and move your mailboxes to a fresh DB.

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JAMAuthor Commented:
Thank you for your response RantCan.  

We're not as concerned about data growth, rather just the unexpected overhead we've been seeing with available drive space going lower (as low as 1% and as high as 6% daily), despite our available whitespace.  Because of that available whitespace, we don't need (and don't want) to archive anything to PST files and unfortunately, we hit our maximum amount of DBs allowed with a Standard license, so the option to move our mailboxes to a fresh DB isn't currently available to us.  An offline defrag is a last resort, as we understand it isn't best practice, although we've done this successfully in the past without any issues.
All that said, thanks to our hybrid environment, we have a plan to move a group of mailboxes to office365, after which we'll move mailboxes between our on-premise databases, which will in turn allow us to empty a couple of databases and create new ones (right now, we can't create a new DB as we've hit the maximum amount of DBs allowed with our Standard license).  And now that we know that small overhead (of available free disk space being used daily, despite the available whitespace) is normal, we're going to prepare to execute this plan earlier than originally anticipated.  Thanks for confirming that.
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