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As shown in the diagram above, hierarchical objects and all the tree indexes remain in MD-blob and DRAM, whereas flattened objects only keeps a little metadata in DRAM and saves all keys and values in DT-blob. In this model, assuming each object consumes 48 bytes for metadata, VOS uses a few more bytes to index object, blob allocator also has its own overhead, overall bytes per object can be around 100 bytes. Based on the previous assumption, a storage server has 800GB 900GB DRAM for metadata, then a server can store up to 8 9 billion 4K files.