Hi, is it accurate to say that
- In 0.20 the Secondary NameNode acts as a cold spare; it can be used to recreate the HDFS if the Primary NameNode fails, but with the delay of minutes if not hours, and there is also some data loss; - in 0.21 there are streaming edits to a Backup Node (HADOOP-4539), which replaces the Secondary NameNode. The Backup Node can be used as a warm spare, with the failover being a matter of seconds. There can be multiple Backup Nodes, for additional insurance against failure, and previous best common practices apply to it; - 0.22 will have further improvements to the HDFS performance, such as HDFS-1093. Does the paper on HDFS Reliability by Tom White<http://www.cloudera.com/wp-content/uploads/2010/03/HDFS_Reliability.pdf>still represent the current state of things? Thank you. Sincerely, Mark
