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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 small header in DRAM and saves all its keys and values in DT-blob. In this model, each object consumes 48 bytes, VOS requires a few extra bytes to index object and allocator also has its own overhead, so the actual bytes per object can be about 100 bytes. If using the same assumption that a storage server has 800GB for MD-blob, then a server can store up to 8 billion 4K files.