diff --git a/Filer-Server-API.md b/Filer-Server-API.md
index b37220b..4553f35 100644
--- a/Filer-Server-API.md
+++ b/Filer-Server-API.md
@@ -47,6 +47,7 @@ You can append to any HTTP API with &pretty=y to see a formatted json output.
 ### notice
 * It is recommended to add retries when writing to Filer.
 * `AutoChunking` is not supported for method `PUT`. If the file length is greater than 256MB, only the leading 256MB in the `PUT` request will be saved.
+* When appending to a file, each append will create one chunk and added to the file metadata. If there are too many small appends, there could be too many chunks. So try to keep each append size reasonably big.
 
 Examples:
 ```bash