HDFS-8852. HDFS architecture documentation of version 2.x is outdated about append write support. Contributed by Ajith S.

(cherry picked from commit fc509f66d814e7a5ed81d5d73b23c400625d573b)

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -847,6 +847,9 @@ Release 2.7.2 - UNRELEASED
     HDFS-8806. Inconsistent metrics: number of missing blocks with replication
     factor 1 not properly cleared. (Zhe Zhang via aajisaka)
 
+    HDFS-8852. HDFS architecture documentation of version 2.x is outdated
+    about append write support. (Ajith S via aajisaka)
+
 Release 2.7.1 - 2015-07-06
 
   INCOMPATIBLE CHANGES

hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HdfsDesign.md

@@ -73,7 +73,7 @@ Applications that run on HDFS have large data sets. A typical file in HDFS is gi
 
 ### Simple Coherency Model
 
-HDFS applications need a write-once-read-many access model for files. A file once created, written, and closed need not be changed. This assumption simplifies data coherency issues and enables high throughput data access. A Map/Reduce application or a web crawler application fits perfectly with this model. There is a plan to support appending-writes to files in the future.
+HDFS applications need a write-once-read-many access model for files. A file once created, written, and closed need not be changed except for appends and truncates. Appending the content to the end of the files is supported but cannot be updated at arbitrary point. This assumption simplifies data coherency issues and enables high throughput data access. A MapReduce application or a web crawler application fits perfectly with this model.
 
 ### "Moving Computation is Cheaper than Moving Data"