> How much memory/JVM heap does NameNode use for each block?
I don't remember the exact number, it also depends on which version of
Hadoop you're using
> http://search-hadoop.com/m/O886P1VyVvK1 - 1 GB heap for every object?
It's 1 GB for every *million* objects (files, blocks, etc.). This is a
good rule of thumb, at least for the 0.20.x/1.0.0 series.
Is there a reason you need a more exact estimate?