Source : https://github.com/trapexit/mergerfs
Download :
https://www.qnapclub.eu/fr/qpkg/798
About :
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.
FEATURES
Runs in userspace (FUSE)
Configurable behaviors / file placement
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 (transparently move file to drive with capacity)
Handles pool of read-only and read/write drives
Can turn read-only files into symlinks to underlying file
Hard link copy-on-write / CoW
supports POSIX ACLs
How it works
mergerfs logically merges multiple paths together. Think a union of sets. The file/s or directory/s acted on or presented through mergerfs are based on the policy chosen for that particular action.