Have you looked at the vfiler migration cmdlets?
PS C:\> Get-NaHelp *VfilerMigrate
Name                                    Api                                     Category
----                                    ---                                     --------
Complete-NaVfilerMigrate                {vfiler-migrate-complete}               vfiler
Get-NaVfilerMigrate                     {vfiler-migrate-status}                 vfiler
Start-NaVfilerMigrate                   {vfiler-migrate-start}                  vfiler
Stop-NaVfilerMigrate                    {vfiler-migrate-cancel}                 vfiler