HDFS is a distributed scalable filesystem written in Java for the Hadoop processing framework. HDFS is not a fully POSIX-compliant filesystem and does not offer a block interface. The reliability of HDFS is of concern as it lacks high availability. The single NameNode in HDFS is a SPoF and performance bottleneck. HDFS is again suitable, primarily storing a small number of large files rather than the mix of small and large files at scale that modern deployments demand.