MOS: Free, open-source NAS OS with Unraid-style parity
MOS boots from a USB stick by default, or installs to an SSD or NVMe drive. Each pool can be a single disk, RAID 0 or 1, a mergerfs pool with optional SnapRAID parity, or a parity array from a MOS Hub plugin (up to 2 parity disks and 28 data disks) where each drive keeps its own filesystem, so drives of different sizes can share one pool. Apps install as Docker containers from MOS Hub templates, alongside LXC containers and QEMU/KVM virtual machines. It is free and open source under the AGPLv3. It started as one developer's personal project, and version 0.5.0 in July 2026 was the first release marked stable; ARM builds are still experimental.
Is MOS right for you?
Choose MOS if: You want to grow a pool from mismatched drives behind parity, like Unraid, but free and open source.
Pros
- Free and open source
- Mixed drive sizes with mergerfs and SnapRAID or a parity array
- Docker templates, LXC and VMs with GPU passthrough
Cons
- Young project; first stable release in mid-2026
- ZFS is a plugin with no web UI
- UEFI boot only; ARM support is experimental
Compare with other NAS OS
See how MOS differs on storage, licensing and what it runs on.
| Spec | MOS | Unraid | TrueNAS | HexOS | ZimaOS | openmediavault | FygoOS |
|---|---|---|---|---|---|---|---|
| Price | Free | From $49 | Free | $199 lifetime | Free, $29 Plus | Free | Free, $199 lifetime |
| Licence | AGPL-3.0 | Proprietary | GPL-3.0 / LGPL-3.0 | Proprietary | Proprietary | GPL-3.0 | Proprietary |
| Based on | Devuan | Slackware | Debian | TrueNAS | Buildroot | Debian | Linux |
| Boots from | USB / SSD / NVMe | USB / SSD / NVMe | SSD / NVMe | SSD / NVMe | SSD / NVMe | USB / SSD / NVMe | SSD / NVMe |
| Storage | XFS, Btrfs, mergerfs, SnapRAID, parity array | Parity array or ZFS | ZFS | ZFS | RAID, ZFS or JBOD | RAID, mergerfs, SnapRAID | ext4, Btrfs or ZFS |
| Mixed drive sizes | Yes | Yes | Each vdev uses its smallest drive | Each vdev uses its smallest drive | Via JBOD, without redundancy | With mergerfs | Not documented |
| Virtual machines | Yes (QEMU/KVM) | Yes | Yes | Yes | Yes (ZVM) | Via plugin (KVM) | Yes (best on x86) |
| Apps | MOS Hub (Docker templates), LXC | Community Apps (Docker) | TrueNAS Apps (Docker) | Curated one-click apps | One-click store (Docker) | Docker Compose plugin | App Center and Docker |
| Architecture | x86 and ARM | x86 only | x86 only | x86 only | x86 only | x86 and ARM | x86 and ARM |
| Min RAM | 4 GB | 4 GB | 8 GB | 8 GB | 4 GB | 1 GB | 2 GB |
| Best for | Unraid-style storage without a licence fee | Growing a pool from mismatched drives | Data integrity, snapshots and replication | TrueNAS without the learning curve | Simple app hosting with little setup | Low-power ARM boards and old PCs | Photo backup and file sharing with little setup |