$SourcePath = "E:\Backup"
$BackupPath = "G:\Backup\GigabyteWinServer"

function Copy-Dir($Source,$Destination){
  $n = New-Item -ItemType Directory -Force -Path $Destination
  Write-Host("Copy Folder: $Source to Folder: $Destination")
  $files = Get-ChildItem $Source -Recurse
  foreach ($f in $files){
    $dest = $f.FullName.Replace($Source,$Destination)
    if ($f.PSIsContainer){
      $n = New-Item -ItemType Directory -Force -Path $dest
    } else {
      if ($f.Length -gt 10000000){
        Start-BitsTransfer -Source $f.FullName -Destination $dest
      } else {
        Copy-Item -Path $f.FullName -Destination $dest
      }
    }
  }
}

function Backup-Data($SourcePath,$BackupPath){
  $sources = Get-ChildItem -Path $SourcePath
  $sources = $Sources | Sort-Object -Property FullName
  $BackupDrive = $BackupPath -replace(':.*','')
  $move = $true
  foreach($f in $sources){
    $Source = $f.FullName
    if ($f -eq $sources[$sources.Length-1]){
      Write-Host("Copying: $f")
      $move = $false
    } else {
      Write-Host("Moving: $f")
      $move = $true
    }
    $foldersize = (Get-ChildItem -path $Source -Recurse | Measure-Object -Property Length -sum).Sum / 1Gb    
    $free = (Get-PSDrive -Name $BackupDrive).Free / 1Gb
    Write-Host("  Backup-Data-Size: $foldersize (free: $free)")
    if ($foldersize -lt $free){
      $Destination = $BackupPath+"\"+$f  
      if (Test-Path -Path $Destination){
        Write-Host("  Target folder exists...checking size")
        $copysize = (Get-ChildItem -path $Destination -Recurse | Measure-Object -Property Length -sum).Sum / 1Gb    
      } else {
       $copysize = 0
      }          
      if ($foldersize -ne $copysize){
        Write-Host("  Source-Path: $Source")
        Write-Host("  Target-Path: $Destination")
        #Copy-Dir -Source $Source -Destination $Destination
      } else {
        Write-Host("  Skipping $Source, as it is already available on destination with identical size.")
      }
      
      if ($move){
        Write-Host("  Finally cleaning up after move")
        #Remove-Item -Recurse -Force $Source
      }
    } else {
      Write-Host("ERROR: Not enough free space on Backup-Drive!")
    }    
  }
}

#main
if (Test-Path $BackupPath){
  if (Test-Path $SourcePath){
    Backup-Data -SourcePath $SourcePath -BackupPath $BackupPath
  } else {
    Write-Host("ERROR: Source Path: $SourcePath isn't available!")
  }
} else {
  Write-Host("ERROR: Backup Path: $BackupPath isn't available!")
}