HDFS-13356. Balancer:Set default value of minBlockSize to 10mb. Contributed by Bharat Viswanadham

(cherry picked from commit 9b5375e0c1ee8c634a5accb7415ec27440543a60)

hadoop-hdfs-project/hadoop-hdfs/src/main/proto/NamenodeProtocol.proto

@@ -43,7 +43,10 @@ import "HdfsServer.proto";
 message GetBlocksRequestProto {
   required DatanodeIDProto datanode = 1; // Datanode ID
   required uint64 size = 2;              // Size in bytes
-  optional uint64 minBlockSize = 3 [default = 0]; // Minimum Block Size in bytes
+  // Minimum Block Size in bytes, adding default value to 10MB, as this might
+  // cause problem during rolling upgrade, when balancers are upgraded later.
+  // For more info refer HDFS-13356
+  optional uint64 minBlockSize = 3 [default = 10485760];
 }