Mergerfs is a union filesystem geared towards simplifying storage and management of files across numerous commodity storage devices. It is similar to mhddfs, unionfs, and aufs.

Some salient features include * Runs in userspace (FUSE) * Configurable behaviors * Support for extended attributes (xattrs) * Support for file attributes (chattr) * Runtime configurable (via xattrs) * Safe to run as root * Opportunistic credential caching * Works with heterogeneous filesystem types * Handling of writes to full drives * Handles pool of readonly and read/write drives