Understanding Automatic Mailbox Distribution
http://technet.microsoft.com/en-us/library/ff477621.aspx

1. Exchange retrieves a list of all mailbox databases in the Exchange 2010 organization.
2. Any mailbox database that’s marked for exclusion from the distribution process is removed from the available list of databases. You can control which databases are excluded.
3. Any mailbox database that’s outside of the database management scopes applied to the administrator performing the operation is removed from the list of available databases.
4. Any mailbox database that’s outside of the local Active Directory site where the operation is being performed is removed from the list of available databases.
5. From the remaining list of mailbox databases, Exchange chooses a database randomly. If the database is online and healthy, the database is used by Exchange. If it’s offline or not healthy, another database is chosen at random. If no online or healthy databases are found, the operation fails with an error.

Excellent article, thank you for taking the time to write it. Once quick question, is there any documentation on how the provisioning procesess decides on malibox location? Is it a simple round robin between availble servers in the same site, or does it look at any statisitics such as iops or such?

Exchange Server 2010 introduced a new feature for automatically assigning a database while provisioning…

If you need to you could use the Exchange_Mailbox WMI class to grab the 2003 mailboxes sizes.

For example, grab all mailboxes larger than 2gb:

$largeMailboxes = Get-WmiObject -NameSpace Root\MicrosoftExchangeV2 -Class Exchange_Mailbox -ComputerName ex2003server | ?{$_.size -gt 2000000}

Then you can see how many mailboxes are in the collection and the total size:

$largeMailboxes | Measure-Object size -sum | select count,sum

Obviously that’s a rough estimate of the total size it will actually be on the other side depending on a number of factors, but if that meets your requirements you can move them in a batch:

$largeMailboxes | %{New-MoveRequest -Identity $_.legacydn -TargetDatabase DB1 -BadItemLimit 100 -BatchName LargeMailboxes}

So, not a full blow script here, but maybe those examples can give you some more ideas.

That’s what I had thought regarding individual mailbox size as a bit of googling had turned up empty. What we plan on doing then is to use the script below, and after a given number of mailboxes have been moved, check to see if any databases are reaching our threshold level. If so, we’ll so as you also mentioned, by suspending them from the pool.

-Brian

Set-AdServerSettings -ViewEntireForest $True
$file = Read-Host “Enter File Path for list of users. Example: C:\Scripts\File.txt”
$batch = Read-Host “Enter Batch Name for easy tracking of move requests. Example: Batch001″
$list = get-content $file
$DB = @{}
foreach ($mailbox in $list) {New-MoveRequest -Identity $mailbox -TargetDatabase $DB –baditemlimit 100 -BatchName $Batch | %{
$DB[$_.database] = $DB[$_.database] + 1
}
}
Get-MoveRequest -Batchname $batch
Write $DB

Thanks for the comment. Yes the New-MoveRequest cmdlet will use this automatic mailbox distribution logic when you do not specify a database using the TargetDatabase parameter.

I’m not aware of any existing scripts that will move a mailbox based on its size, but if you want to give me more details I can try to give you some ideas.

An additional question: Do you know of a PowerShell command that would also analyze the size of each individual mailbox and factor that in when assigning a database withing the DAG?

Thank you,
Brian

I recently needed to write a script to spread mailboxes in Exchange Server 2010 alphabetically across…