Updated Erasure coding for warm storage (markdown)

Erasure-coding-for-warm-storage.md

@@ -21,6 +21,8 @@ The default command is `ec.encode -fullPercent=95 -quietFor=1h`. It will find vo
 ### Data Repair
 The default command is `ec.rebuild -force`. If disk fails or server fails, some data shards are lost. With erasure coding, we can recover the lost data shards from remaining data shards.
 
+The data repair happens for the whole volume, instead of one file at a time. It is much more efficient.
+
 ### EC data balancing
 With servers added or removed, some data shards may not be laid out optimally. For example, one volume's 5 data shards could be on the same server. If the server goes down, the volume would be unrepairable or part of the data is lost permanently. 
 
@@ -29,6 +31,6 @@ The default command is `ec.balance -force`. It will try to spread the data shard
 ## How the read works?
 When all data shards are online, the read are randomly assigned to one volume server (A) that has at least one data shard. Server A will read its copy of index file, and locate the volume server (B), and read from server B for the file.
 
-
+In case of missing data shards or read failures from server B, server A will try to collect as many pieces of data as possible from the remaining servers, and compute the required data.
 
 ## Read Performance