diff --git a/docs/dd_pfs.md b/docs/dd_pfs.md
index 70d8913..1cf6c7c 100644
--- a/docs/dd_pfs.md
+++ b/docs/dd_pfs.md
@@ -31,7 +31,11 @@
 	Status    ChunkStatus
 	// Total size of chunk in bytes
 	Size      int
-	// Number of bytes committed on disk
+	// Number of bytes committed to disk
 	Committed int
 }
 ```
+Total of 16 + 3 * 32 = 112 bytes are needed to store single chunk metadata. On top if this thread-safe hash map backed ChankInfoStore structure will be built with two Load and Store methods. Store method will update in memory hash map and also append it to transaction logs. Background process will compact transaction logs periodically and persist full hash map contents on disk.
+
+Controller will not persist any data locally. Instead it will receive state of chunk servers periodically using heart beats. This makes it is easier to keep metadata stored in controller and chunk servers consistent.
+