Xenserver live migration not possible for VM's with base copies

Hello, 

We are in process of live migrating VM's from Xenserver 6.1/6.2 to Xenserver 7.6. While initiating  the migration, the VM's that have orphaned base copies files fails. Further, it creates additional base copy as it tries to create snaphost and as the migration process fails it does not delete the snaphot file. We have local storage setup as EXT partition. Coalesce  does not work on ext partition. Is there any way we can remove the orphaned base copies  and live migrate the VM's.