From the Wikipedia article on Lustre File Systems:
Lustre is a type of parallel distributed file system, generally used for large-scale cluster computing. The name Lustre is a portmanteau word derived from Linux and cluster. Lustre file system software is available under the GNU General Public License (version 2 only) and provides high performance file systems for computer clusters ranging in size from small workgroup clusters to large-scale, multi-site clusters.
Because Lustre file systems have high performance capabilities and open licensing, it is often used in supercomputers. At one time, six of the top 10 and more than 60 of the top 100 supercomputers in the world have Lustre file systems in them, including the world’s #2 ranked TOP500supercomputer, Titan in 2013.
Lustre file systems are scalable and can be part of multiple computer clusters with tens of thousands of client nodes, tens of petabytes (PB) of storage on hundreds of servers, and more than a terabyte per second (TB/s) of aggregate I/O throughput. This makes Lustre file systems a popular choice for businesses with large data centers, including those in industries such as meteorology, simulation, oil and gas, life science, rich media, and finance.