How to upgrade hadoop cluster?

Question

I want to upgrade my cluster ,in doc,one of step is backup namenode dfs.namenode.name.dir directory.
I have two directories defined in hdfs-site.xml, should I backup them all ,or just one of them?

dfs.namenode.name.dir
file:///data/namespace/1,file:///data/namespace/2

Answer 1

Backing up one of them is sufficient, but do check if both their contents are same and backup the more recent one (a mount may lag behind if it had a failure earlier, for ex.).