Well, rather topically, there's MapR. Depending on the desired scale and level of fidelity to real-filesystem semantics, one might also count Gluster, Ceph, and

Well, rather topically, there's MapR. Depending on the desired scale and level of fidelity to real-filesystem semantics, one might also count Gluster, Ceph, and Lustre. Don't know if PVFS is still around. There are more proprietary offerings from IBM (GPFS/SpectrumScale), EMC, NetApp, etc. plus a plethora of startups. There are other object stores that don't make a pretense of being filesystems. Alternatives abound. BTW, "hundreds of terabytes on hundreds of machines" isn't interesting territory any more. Most people's needs are far smaller, so HDFS isn't much help. Those who need more generally need much more, so HDFS isn't much help again. Richer semantics are nice either way. Imagine thousands of machines with dozens of terabytes each and you might start to see the problems with HDFS's design (though you'll still be far short of the domain I work in).