Exchange 2010 DAG - Backup fail during seeding

Hi

We are running Exchange 2010 SP2 with 2 MailBox servers, 2 CAS & HUB. We have a DAG consisting of 6 Databases. Average Database size is 400GB.

On our DR site, we have configured same number of Exchange servers. Successfully added 2 members to existing DAG. When tried to add the database copy, backup start failing and database got unmounted because log files drive was full. 

Questions: Is backup is expected to fail during seeding?

Regards

Ahmed