Exch 2003 - 2007 migration  mailbox database best practices

someITGuy used Ask the Experts™
We are planning to migrate from Exchange 2003 to Exchange 2007. We currently have 5 storage groups with 4 mailbox databases on 2 servers. Following Microsoft's recommendation, we are moving to 20 storage groups with 1 mailbox database each on a cluster managed server (CMS).

Realizing that Exchange 2003 has a 50GB recommended mailbox database limit & Exchange 2007 has a 200GB recommended mailbox database limit, we want to make the new mailbox databases no bigger than 100GB each to accommodate future growth.

Our current largest mailbox database on Exchange 2003 is 450GB and a couple more are over 100GB. We are trying to come up with a strategy on how to divide up the mailbox databases when we move them to Exchange 2007. Our largest individual mailbox within a current mail database is 12GB and we have over 300 users with mailboxes larger than 1GB.

Is it better to group all the big mailbox users in their own mailbox databases (keeping them under 100GB) or is it better to mix them in with regular users?

We currently have no mailbox policies in place, we hope to implement them in the near future pending very slow management approval but the policies will not be in place prior to the Exchange 2007 migration. We MAY have 2 policies, one for very large mailbox users and one for regular users that has a limit of 350GB per mailbox.
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Top Expert 2010

I think your best bet is to move mailboxes in groups according to mailstore.

Single Instance Storage is only kept in tact if the mailboxes are moved from the same store to the same store.

For example if you have 100 users in a store move them together to the same store to maintain SIS


We cannot do that with the the current mailbox databases that are over 100GB in size. Our biggest current mailbox database is 450GB & we MUST chop it up into 5 mailbox databases totaling less than 100GB.

So the question is still out there:

Is it better to group the greater that 1GB mailboxes in separate mailbox databases (up to 100GB total size) from the regular (less than 350MB) users or is it better to mix in the large mailbox users with the regular users?
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Top Expert 2010

We MUST you chop it up?
Exchange 2007 will support 450GB mailboxes.

It doesn't really make any difference how you group the databases.
If you move them away from the databases you are in now then you will loose single instance storage and therefore increase the mailstore sizes.
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We were told by a Microsoft engineer (and Microsoft documentation) we should not go over 200GB in Exchange 2007 and that after a 3 day onsite analysis they recommended keeping the initial size under 100GB. This was before I arrived here & I do not have access to the MS engineer at this point.

I think these numbers are driven by recovery times if we have to restore a database....
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Top Expert 2010

They recommend you don't go over 200GB in a single mailbox store but it will go up to 2TB
I went back to Microsoft & got some clarification, they say SIS is not an issue with Exchange 2007. THe issue I face is the ability to quickly recover a mailbox database in an acceptible period of time. So I am paring the mailbox databases down to under 100GB.

Here is what Microsoft said:  

So the guy is not exactly right…  Theoretically, Exchange 2007 will support a database size of 16 Terabytes.  So if you were to put just one user in his own database, that user can theoretically grow up to 16 TB.  The problem of course is backing it up and restoring it.  We don’t really have a good way of doing that.  That’s why we recommend the following.


100GB Max databases for Stand Alone Exchange 2007 servers.

200GB Max databases for CCR Exchange 2007 Servers.


As far as Single Instance Storage, not even a blip on Exchange 2007 anymore.  We say not to even consider SIS when planning your Exchange deployment.  ;-)


There a good link to SIS below.


Hope this helps.  ;-)



Exchange 2007 Max Database Size
The ESE database engine can maintain a file up to 16 terabytes


Single Instance Storage
The move to multiple databases per server, along with the reduction in space savings due to items being deleted over time, means that the space savings from SIS are quite small for most customers. Because of this, we've long recommend that customers ignore SIS when planning their storage requirements for Exchange.


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