Update 4.storage-config.md (#1648)

* Update 4.storage-config.md

* Update 4.storage-config.md

* Update 4.storage-config.md

docs-2.0/5.configurations-and-logs/1.configurations/4.storage-config.md

@@ -199,4 +199,8 @@ When the query starting from each vertex gets an edge, truncate it directly to a
 
 ## Storage configurations for large dataset
 
+!!! warning
+
+    One graph space takes up at least about 300 MB of memory.
+
 When you have a large dataset (in the RocksDB directory) and your memory is tight, we suggest that you set the `enable_partitioned_index_filter` parameter to `true`. The performance is affected because RocksDB indexes are cached.