HDFS block storage

[John Lilley]

I was looking at the HDFS block storage and noticed a couple things (1) all 
block files are in a flat directory structure (2) there is a "meta" file for 
each block file.  This leads me to ask:
-- Where can I find good reading that describes this level of HDFS internals?
-- Is the flat storage sufficient to handle millions of blocks?
-- What is in the meta file?  Why isn't it just a header or trailer on the data 
file?
Thanks
John