The reason for using 100 node hBase clusters is not because HBase does not scale to larger sizes. It is because it is easier to do hBase/HDFS software upgrades on a rolling fashion without bringing down your entire service. Another reason is to prevent a single NameNode to be a SPOF for the entire service. Also, HBase is being used for various services (not just FB messages) and it is prudent to have a cookie-cutter approach to setting up numerous HBase clusters based on a 100-node pod approach. The number 100 is adhoc, we have not focussed on whether 100 is optimal or not.
