List out some limitation of Hadoop.

• Write-once model
• Plan to support appending-writes
• A namespace with an extremely large number of files exceeds Namenode’s capacity to maintain
• Cannot be mounted by exisiting OS
• Getting data in and out is tedious
• Virtual File System can solve problem
• Java API
• Thrift API is available to use other languages
• HDFS does not implement / support
• User quotas
• Access permissions
• Hard or soft links
• Data balancing schemes
• No periodic checkpoints
• Namenode is single point of failure
• Automatic restart and failover to another machine not yet supported