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@@ -34,4 +34,18 @@ Filer provides a convenient and common abstraction that can be used to provide n
 
 ## S3 service
 
-This optional service provides AWS style S3 buckets, similar to the filer service. It can be started separately, or together with the filer.
\ No newline at end of file
+This optional service provides AWS style S3 buckets, similar to the filer service. It can be started separately, or together with the filer.
+
+## Volume Concept
+
+The volume in SeaweedFS means a single actual file consists of many small files. When master starts, it configures the volume file size, default to 30GB. At the beginning, there are 8 volumes created.
+
+## Collection Concept
+
+One collection is basically a group of volumes. If no volume in the collection, the volumes will be auto created. 
+
+The collection can be deleted quickly, since it is just simply removing all the volumes in the collection. 
+
+If you want to use S3 service, one bucket has a dedicated collection. So removing a bucket is also fast.
+
+Since one collection needs to have several volumes, and each volume is 30GB by default, you may run out of disk space quickly. You can reduce the volume size to 1GB or 512MB.