There will be three different object forms in DAOS:
Hierarchical object
Hierarchical object in memory bucket
Flattened object
This diagram shows the DAOS object forms, all elements in the blue rectangle are stored in DT-blob, they only consume memory during I/O processing, they can be evicted from DRAM if the system is under memory pressure. All the elements outside the rectangle are stored in MD-blob, it means that they stay in DRAM permanently when the pool is opened.
When an object is created, it is always hierarchical, but it can either be in MD-blob or in DT-blob (memory bucket), it can be flattened by flattening service late if it is a WORM object. If a hierarchical object is put in MD-blob, then it will be pinned in DRAM, otherwise it is loaded into DRAM on demand.
