We are using MongoDB GridFS to create a document archive. I am creating a sharded cluster at our Primary DataCenter. I need a working backup at our offsite Disaster Recovery DataCenter. This will be a very large database, ~6TB. I will be adding 20k new documents daily. I need to be able to take incremental backups at the end of our batch cycle and apply them to the offsite cluster. We do not want to use replication because we want the clusters to be entirely independent, but essentially identical. We will never delete from the collection. We are running Red Hat.
Does anyone have any suggestions about how to keep the databases in sync?