 HDFS is not fully POSIX-compliant, because the requirements for a POSIX file-system differ from the target goals of a Hadoop application.The trade-off of not having a fully POSIX-compliant file-system is increased performance for data throughput and support for non-POSIX operations such as Append.In May 2012, high-availability capabilities were added to HDFS, letting the main metadata server called the NameNode manually fail-over onto a backup.