When DAOS runs in MD-on-SSD mode, it writes metadata for twice: it packs all metadata changes to contiguous buffer and writes to WAL during I/O handling, then flushes in-place changes of metadata from DRAM to MD-blob periodically by checkpointing service. The write amplification can be reduced if multiple in-place metadata changes land in the same set of dirty pages.
When WORM object support and flattening service are added to storage engine, metadata of WORM object will be written for three times, because metadata will be serialized and written to DT-blob by flattening service. This may impact the overall performance and endurance of SSD.