diff --git a/Master-Server-API.md b/Master-Server-API.md
index 58b03ec..ebd7f39 100644
--- a/Master-Server-API.md
+++ b/Master-Server-API.md
@@ -20,7 +20,7 @@ curl "http://localhost:9333/dir/assign?dataCenter=dc1"
 
 | Parameter | Description | Default |
 | ---- | -- | -- |
-| count | how many file ids to reserve | 1 |
+| count | how many file ids to assign. Use `<fid>_1`, `<fid>_2` for the extra assigned file id. e.g. 3,01637037d6_1, 3,01637037d6_2 | 1 |
 | collection | required collection name | empty |
 | dataCenter | preferred data center | empty |
 | rack | preferred rack | empty |