Reduce metadata storage costs, persist metadata in metadata storage, and dynamically load into memory

[leonrayang]

Is your feature request related to a problem? Please describe. Reduce metadata storage costs, persist metadata in metadata storage, and dynamically load into memory Not all metadata is accessed frequntly, the cost of metadata in EB data cluster is absolutely considerable

Describe the solution you'd like compatibility , performance, statbility take Rocksdb into consideration

[Huweicai]

Maybe we can expose this feature by adding a switch for volume, sometimes some volumes are only used for data backup, may no access traffic at all.