LizardFS

LizardFS is an open source distributed file system that is POSIX-compliant and licensed under GPLv3. It was released in 2013 as fork of MooseFS. LizardFS is also offering a paid Technical Support (Standard, Enterprise and Enterprise Plus) with possibility of configurating and setting up the cluster and active cluster monitoring. 
LizardFS is a distributed, scalable and fault-tolerant file system. The file system is designed so that it is possible to add more disks and servers “on the fly”, without the need for any server reboots or shut-downs.
Description.
LizardFS makes files secure by keeping all the data in multiple replicas spread over the available servers. This storage is presented to the end-user as a single logical namespace. It can also be used to build space-efficient storage because it is designed to run on commodity hardware. It has applications in multiple fields and is used by institutions in finance, telecommunications, medicine, education, post-production, game development, cloud hosting services, and others.
Hardware.
LizardFS is fully hardware agnostic. Commodity hardware can be utilized for cost efficiency. The minimum requirements are two dedicated nodes with a number of disks, but to obtain a high available installation at least 3 nodes are needed. This will also enable the use of erasure coding.
Architecture.
LizardFS keeps metadata (e.g. file names, modification timestamps, directory trees) and the data separately. Metadata are kept on metadata servers, while data is kept on chunkservers. 
A typical installation consists of: