Regarding the scenario of small I0 write cache in Huawei's distributed storage multi-level cache technology, which of the following order is correct?
1.Write to the WAL log area based on the SSD slow disk, and return to the host to complete the write operation
2.When the memory write cache reaches a certain water level, the data starts to be flushed down
3.Data writing to RAM-based Write Cache
4.Small IOs will be written to the SSD cache of the node first, waiting to be aggregated into large IOs and then written to HDD