One mount.
Many disks.
Explicit rules.

PolicyFS unifies multiple storage paths under a single FUSE mountpoint. Routing rules control exactly where reads and writes go — and an optional SQLite index keeps your HDDs asleep during metadata-heavy workloads.

Get started → Read the docs
SSD ssd1 ssd2 HDD hdd1 hdd2 hdd3 pfs router & write policies SQLite metadata index deferred event log /mnt/media unified view

Features

Storage behavior you can reason about

Policy-based routing

Route reads and writes by path pattern — one rule for photos/**, another for everything else. Write policies (first_found, most_free, least_free) control target selection. Path-preserving mode keeps related files on the same disk.

SQLite metadata index

Mark a storage path indexed: true and readdir/getattr calls are served from a local SQLite database — no disk spin-up. Metadata mutations (delete, rename, chmod) are deferred to an event log and applied later by pfs prune.

Built-in maintenance cycle

pfs move tiers files from fast SSD to bulk HDD. pfs prune applies deferred mutations. pfs index refreshes metadata. pfs maint runs all three in the right order — ready for a daily systemd timer.

Architecture

How pfs handles a filesystem call

1

POSIX syscall

Your application opens a file normally — pfs is transparent to userspace.

2

FUSE dispatch

The kernel forwards the call over FUSE to the running pfs daemon process.

3

Routing & index

The router matches the path to a rule. Metadata is served from SQLite; HDDs stay asleep.

4

Physical I/O

Data reads and writes hit the physical storage directly via a cached file descriptor.

Comparison

pfs vs mergerfs

mergerfs is a mature, battle-tested FUSE union filesystem with broad POSIX coverage and a large install base. pfs is a narrower tool focused on making storage placement and metadata access explicit. If you need maximum compatibility or are running complex workloads, mergerfs is likely the better fit.

Feature pfs mergerfs
FUSE-based storage pooling ✓ ✓
Path-pattern routing rules ✓ —
Multiple write target policies ✓ ✓
SQLite metadata index (HDD sleep) ✓ —
Deferred metadata mutations ✓ —
Built-in tiered storage mover ✓ —
POSIX feature coverage partial ✓
Maturity & ecosystem newer established

pfs trades POSIX breadth for explicit, inspectable behavior. mergerfs covers more edge cases and has a much longer track record.

Configuration

One YAML file, one mount

A minimal two-tier setup: SSD as a fast write cache, HDDs as indexed archive storage. 

# /etc/pfs/pfs.yaml
mounts:
  - name: media
    mountpoint: /mnt/media

    storage_paths:
      - id:   ssd1
        path: /mnt/nvme/cache

      - id:      hdd1
        path:    /mnt/hdd1/media
        indexed: true

      - id:      hdd2
        path:    /mnt/hdd2/media
        indexed: true

    routing_rules:
      - match:         "**"
        targets:       [ssd1, hdd1, hdd2]
        write_policy:  most_free

Install on Debian / Ubuntu

Package and systemd units included. Runs as an unprivileged service.

apt install pfs Install guide →