Scott Schnoll covered a very interesting question on his blog yesterday and I wanted to make sure you saw it. The question is:
When you're making a backup off the passive copy, what happens to the transaction logs? A common task during Exchange-aware backups is the truncation of transaction log files after the backup has completed successfully. The replication feature in Exchange guarantees that logs that have not been replicated are not deleted.
To learn the answer to that question and see what happens during VSS backups of the storage group copy, go here.