For the number of file the OP has why not just use a traditional filesystem and solr to index the pdf data. You get to search inside of the files for relevant information?
Even when storage is in NFS, Cassandra can still be quite useful as a file
catalog. Your physical storage can change, move etc. Therefore, it's a good
idea to provide mapping of logical names to physical store points (which in
fact can be many). This is a standard technique used in mass storage.
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