The master nodes have significantly different storage and memory requirements than the slave nodes. The following paragraphs discuss storage considerations.
Storage Options
We recommend using dual NameNode servers: one primary and one secondary. Both NameNode servers should have highly reliable storage for their namespace storage and edit log journaling. Hardware RAID and/or reliable network storage are justifiable options.
The master servers should have at least four redundant storage volumes, some local and some networked.
Multiple vendors sell NAS software. It is important to check their specifications before you invest in any NAS software.
Storage Options for ResourceManager Servers
ResourceManager servers do not need RAID storage because they save their persistent state to HDFS. The ResourceManager server can actually be run on a slave node with a bit of extra RAM. However, if you use the same hardware specifications for the ResourceManager servers and the NameNode server, you retain the possibility of migrating the NameNode to the same server as the ResourceManager. If there is a NameNode failure, a copy of the NameNode’s state can be saved to network storage.
