BlackHole is an data de-duplicating network block device that also supports mirroring, snapshots, and support for multiple LUNs using the same data store. It is filesystem agnostic and has been tested with ext2/3/4, NTFS, ReiserFS, and the Oracle Cluster File System (OCFS2). It supports encryption, compression, and multiple storage backends. The hashing scheme used is user configurable. The program exports an NBD device which can be mounted in Linux and GNU/Hurd.
Skylable SX is a reliable, powerful, fully distributed cluster solution for your data storage needs. It can aggregate the disk space available on multiple servers and merge it into a single storage system. The cluster makes sure that your data is always replicated over multiple nodes (the exact number of copies is defined by the sysadmin) and synchronized. It has built-in support for deduplication, client-side encryption, on-the-fly compression, and much more.