Dave from the looks of your diskpoolnumbers your migrationproces can't
follow, lower your migration settings so that it kicks of earlier or get
more concurrent migrations. Also if you don't do it yet lower your
migrationsettings during a nonbackupperiod to the bottom and reset them
after your primary pool is drained (this way you start each backupsession
with an emty primary pool). Hope this helps.
Greetings, Koen.