Please explain Backup node in Hadoop?
Backup node maintain same name-space in memory as that of primary name-node, so it’s RAM requirement is same as Name-node. In Secondary name-node and checkpoint node, checkpoint is created by downloading fsimages and edit logs on their local file system from active primary name-node and merges these these edit logs files and new fsimgaes copy is saved in local file system. But unlike secondary name-node, backupnode does not need to download fsimage and edit logs from active primary name-node to create a checkpoint, as it already has an up-to-date copy of namespace in it’s own main memory. So creating a checkpoint in backup node is just to save a copy of namespace from main memory to local file system.