diff --git a/Tiered-Storage.md b/Tiered-Storage.md
index 3cfb2b9..1be4b89 100644
--- a/Tiered-Storage.md
+++ b/Tiered-Storage.md
@@ -27,5 +27,5 @@ fs.configure -locationPrefix=/buckets/ssd_ -disk=ssd -apply
 
 https://github.com/chrislusf/seaweedfs/wiki/Path-Specific-Configuration
 
-For now, ssd volumes needs to be manually moved from ssd directories to hdd directories, if you want to change the disk type.
+For now, an ssd volume needs to be manually moved from ssd directory to hdd directory, if you want to change the disk type of a volume.