Generally its believed that RDBMS scales better vertically while nosql are designed specifically to scale horizontally.
What kind of databases would be better fit for this kind of hardware http://www.dell.com/us/enterprise/p/dell-compellent-storage-center/pd.aspx
which can scale up to many hundred TBs.
As nosql databases are typically designed to be run on commodity servers then what should be the specs of that commodity server considering a very high load on database.
And what would be limit of RDBMS hardware node.. considering that enough RAM is available to have indexes (not dataset) in memory all the time.
While NOSQL has not hard requirement of indexes in RAM (but of course its recommended).
It would be also very interesting to know what are best fit for SAN devices? like http://www-03.ibm.com/systems/storage/disk/ds3500/index.html which can hold many hundred TBs at same place.