message: rafs: v6 must have local blobcache configured
  Rafs v6 must store its chunks' info into local
  blobcache. So we must configure blobcache in the
  rafs conf file.
  Check it strictly.
diff: @@ -254,6 +254,13 @@ impl Rafs {
  .as_secs(),
  };
  + // Rafs v6 does must store chunk info into local file cache. So blob cache is required
  + if rafs.metadata().is_v6() && conf.device.cache.cache_type != "blobcache" {
  + return Err(RafsError::Configure(
  + "Rafs v6 must have local blobcache configured".to_string(),
  + ));
  + }
  +
  rafs.ios.toggle_files_recording(conf.iostats_files);
  rafs.ios.toggle_access_pattern(conf.access_pattern);
  rafs.ios
  