They don't go in ram. You have one 64 bit refcount number for every 64MB of storage irrespective of how much is deduplicated; this is a reduction factor of 8M,

They don't go in ram. You have one 64 bit refcount number for every 64MB of storage irrespective of how much is deduplicated; this is a reduction factor of 8M, or 128k per terabyte stored. This largely exists so you can avoid doing extra work on free.