Exchange Mailbox Batch Migration with Intelligent Mailbox Balancing

New-MailboxBatchMigrationCSV.ps1

#requires -version 3.0
#requires -pssnapin Microsoft.Exchange.Management.PowerShell.E2010

<#
.SYNOPSIS
Generates a CSV that can be used with the BatchMigration process
.DESCRIPTION
This script generates a CSV from a list of mailboxes for local migrations. Its primary use is to allow for custom mailbox distribution methods, such as by least-full database or round-robin
This is primarily meant for greenfield migrations where all databases are of similar configuration, and not heterogeneous database environments.
.NOTES
Must be run on a computer with Exchange Management Shell installed due to serialization issues and byte conversion. 
I could make it work remotely but it would require some ugly regex work on the serialized objects since default Exchange config doesn't allow scripts to be run remotely
.EXAMPLE
New-MailboxBatchMigrationCSV.ps1 -Identity (get-mailboxdatabase  server1 | get-mailbox) -targetdatabase newdatabase* | export-csv "$home\desktop\mailboxdb.migrationbatch.csv"

Generate a batch migration CSV from an old mailbox database to databases newdatabase01, newdatabase02, newdatabase03, etc.

.EXAMPLE
$csvpath="C:\scripts\migrations\Group1.csv"
New-MailboxBatchMigrationCSV.ps1 -Identity (import-csv $csvpath).emailaddress -TargetDatabase Tinamail* -AutoMDBMethod leaststorageused -ShowDatabaseSizeDelta | export-csv "$csvpath.migrationbatch.csv"

Take a csv of email Addresses and generate a migrationbatch CSV based on leastStorageUsed algorithm

#>

#Uncomment this and trailing } to make into a command rather than a script
#function New-MailboxBatchMigrationCSV {
    [CmdletBinding()]
    param(
        #Identity of the mailbox to migrate. May pass one or more email addresses,aliases,identity strings,or mailbox objects.
        [Parameter(Mandatory,ValueFromPipeline,ValueFromPipelineByPropertyName)]$Identity,
        #Candidate Target Mailbox Databases. Leave blank to use all relevant databases.
        [String[]]$TargetDatabase,
        #Database Selection Method to use
        #Default is LeastStorageUsed
        #LeastStorageUsed: Select databases based on least storage used, resulting in even distribution by GB
        [String]$AutoMDBMethod='LeastStorageUsed',
        #Outputs the estimated final database sizes, in KB. This uses Write-Host so as not to interfere with the pipeline
        [Switch]$ShowDatabaseSizeDelta
    )

    begin {
        #If no databases were specified, get all databases
        if (!($targetDatabase)) {
            $targetDatabase = (Get-MailboxDatabase).Name
        }

        #TODO: Add ExcludeFromProvisioning Logic

        #If we are doing 'leaststorageused', get the candidate mailbox sizes and set up the database size hashtable
        if ($AutoMDBMethod -match 'leastStorageUsed') {
            $mailDBSizeTable = @{}
            foreach ($TargetDatabaseItem in $TargetDatabase) {
                foreach ($mailDB in (Get-MailboxDatabase $TargetDatabaseItem -status | sort name)) {
                    #Generate a simple hashtable entry for each database for the total curent "used" size of the database
                    $mailDBSizeTable.Add($mailDB.Name,($mailDB.DatabaseSize.toKB() - $mailDB.AvailableNewMailboxSpace.toKB()))
                }
            }
        }

        #If ShowBeforeAfterSizes, take a snapshot of the DBSizeTable
        if ($ShowDatabaseSizeDelta) {
            $mailDBSizeTableBefore = $mailDBSizeTable.clone()
        }
    }
    process {
        $i = 1
        foreach ($IdentityItem in $Identity) {
            write-progress "Evaluating $IdentityItem mailbox placement" -PercentComplete (($i/$identity.count)*100)

            $mbox = get-mailbox $IdentityItem
            
            if ($mbox) {
                $mboxStats = get-mailboxstatistics $IdentityItem
                
                #First Determine the candidate mailbox database
                $selectedDatabase = ($mailDBSizeTable.GetEnumerator() | sort Value | select -first 1).Name

                [PSCustomObject]@{
                    EmailAddress = $mbox.PrimarySmtpAddress
                    TargetDatabase = $selectedDatabase
                }

                #Add the projected mail to be added to the database total, for use in the next evaluation
                $mailDBSizeTable[$selectedDatabase] = $mailDBSizeTable[$selectedDatabase] + $mboxStats.TotalItemSize.Value.ToKB()
                
            }
            $i++
        }

        #Show the final database totals if requested
        if ($ShowDatabaseSizeDelta) {
            $strDBSizes = $mailDBSizeTable.GetEnumerator() | foreach {
                [PSCustomObject]@{
                    Name = $_.Name
                    Before = $mailDBSizeTableBefore[$_.Name]
                    After = $_.Value
                    Growth = ($_.Value - $mailDBSizeTableBefore[$_.Name])
                    PercentGrowth = [Math]::Round((($_.Value / $mailDBSizeTableBefore[$_.Name])-1)*100)
                } 
            } | sort name | format-table | out-string
            
            
            write-host ""
            write-host -ForegroundColor Green "===Estimated Database Sizes after Migration==="
            write-host -ForegroundColor Green $strDBSizes
        }
    } 
    
#} #Function