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
Configurable behaviors / file placement
Ability to add or remove filesystems at will
Resistance to individual filesystem failure
Support for extended attributes (xattrs)
Support for file attributes (chattr)
Runtime configurable (via xattrs)
Works with heterogeneous filesystem types
Moving of file when filesystem runs out of space while writing
Ignore read-only filesystems when creating files
Turn read-only files into symlinks to underlying file
Hard link copy-on-write / CoW
Support for POSIX ACLs
Misc other things
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.
trapexit/mergerfs: a featureful union filesystem
https://github.com/trapexit/mergerfs
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