How to migrate mailboxs from exchange 2007 to exchange 2010????

we migrated all our exchange 2007 mailboxes to exchange 2010.  the problem is that the database size on 2007 is 143GB and we made 5 databases on exchange 2010 and migrated the users to their respective mailbox databases on 2010 and then when i add up the 5 database sizes on 2010 and they are not the same total size as the DB on 2007.  WHY???

wheni was doing the migration i received no errors on the migration at all.

what is going on?

on the 2007 we had 43GB of white space so that would leave 100GB for mail but after we migrated all the mailboxes to 2010 the 5 databases add up to only about 50GB.

what is going on and how do i check to make sure that all mail transfered over?
amoosAsked:
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tjc123Connect With a Mentor IT DirectorCommented:
If you want an accurate listing of how much mail you have, run the following command in Powershell on your Exchange server which will output a CSV file to the C: drive of your Exchange server.  Import it into Excel as a Text file, sum up the size column, and you will see how much mail you have:

Get-MailboxStatistics | Sort-Object TotalItemSize -Descending | ft DisplayName,@{label="TotalItemSize(KB)";expression={$_.TotalItemSize.Value.ToKB()}},ItemCount > c:\test.csv
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Paul MacDonaldDirector, Information SystemsCommented:
There's a lot of overhead in an EDB database - a lot of transactional data that isn't mail, but is needed to make sure no mail is lost.  When you moved the databases, all that overhead was left behind. Give it a few months and your databases will be big again.
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Suliman Abu KharroubIT Consultant Commented:
The database on exchange 2007  contains white space, when  it is moved to exchange 2010 the white space  is no longer on the database.

It is normal.


To calculate the actual size on database without white space check this:

http://technet.microsoft.com/en-us/library/aa996139(v=exchg.65).aspx
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tjc123IT DirectorCommented:
It is very important that your maintenance schedule is running and freeing up as much whitespace as possible or your EDB files for each of your information stores that you have mailboxes on will grow out of control.  This article is for 2007, but it applies to 2010, as well:

http://www.simple-talk.com/sysadmin/exchange/monitoring-and-scheduling-exchange-2007-database-online-maintenance/
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amoosAuthor Commented:
ok, i guess i am just not understanding.  if i have a 143GB database with 43GB of white space that would mean that i have 100GB of mail right or wrong?

after the migration to 2010 i only have about 50GB that came over, what happen to the other 50GB?

is it normal to have this type of result?
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Paul MacDonaldDirector, Information SystemsCommented:
Yes, this is pretty normal.  "White space" is just space reserved for future mail - there's no actual data stored there.  The rest is overhead, like I said.

You moved the mailboxes via the PowerShell command line, right?  And you didn't receive any errors?
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amoosAuthor Commented:
no i moved the mailboxes through the exchange 2010 new local move request, is this the wrong way to do it?
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amoosAuthor Commented:
i did not receive any errors of any kind when i moved all 1700 mailboxes
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tjc123IT DirectorCommented:
Exchange doesn't like to let go of space it previously used, despite archiving or deleting mailboxes.  Think of it as a big file cabinet that physically grows to accommodate new space.  Even if you throw out the files inside, it doesn't change the physical dimensions of the file cabinet.  To alleviate the physical component of size, you create a new information store and just move user mailboxes over to the new store (new file cabinet) and let it grow again.  The key is controlling the growth of the physical file cabinet through maintenance schedules on the information store per my previous link.
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tjc123IT DirectorCommented:
Using the EMC instead of Powershell is just fine.
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amoosAuthor Commented:
ok.  because all of this was done on a R&D enviornment and we are getting ready to do this migration on our production enviornment but it scared us a lot to see that only 50GB out of 143GB came over and there were no errors.

pre migration are there any steps to ensure that all mail comes over?
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Paul MacDonaldDirector, Information SystemsCommented:
Have people look?

That said, if you don't get any errors, you'll be okay.
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