Anyone building a NAS from a recycled computer or a dedicated case has to choose the operating system, and that choice matters more than the hardware. The three names you meet most often are TrueNAS, Unraid and OpenMediaVault. All three share files on the network and offer a web interface, but they start from different philosophies about disk management, and that is where the decision is made.
TrueNAS: ZFS at the core
TrueNAS is built around ZFS. It exists as a Linux-based edition, now the main line, while the long-standing FreeBSD version has been gradually set aside by the developer. Its strength is data integrity: checksums on every block, regular scrubs, snapshots and replication are fully managed from the interface.
What this means:
- disks are organised into redundant vdevs, mirrors or RAIDZ, with ZFS's constraints on expansion;
- disks within a vdev should be the same size, otherwise the extra space is wasted;
- RAM is used as cache, so more memory means better performance;
- applications install as containers from the interface, and virtual machines are available too.
It is the natural choice when the priority is never losing or corrupting data and you accept planning the disk layout in advance.
Unraid: mixed disks, separate parity
Unraid takes an original approach. Each data disk keeps its own independent file system, and one or two extra disks hold parity calculated across all the others. If a disk fails, parity lets you rebuild it; if more disks fail than parity protects, you lose only the data on the failed disks, not the whole array.
Practical consequences:
- you can mix disks of different sizes, the only constraint being that the parity disk must be at least as large as the biggest data disk;
- the array grows one disk at a time;
- unused disks can stay spun down, because a file lives entirely on a single disk: useful for power consumption;
- write performance on the array is limited, which is why an SSD pool is used as cache or for the most active data.
Unraid is a commercial product with a paid licence, tied to the USB stick it boots from. It integrates Docker and virtual machines with a very rich application catalogue. It suits people who accumulate disks over time and mainly store media files.
OpenMediaVault: Debian with an interface
OpenMediaVault is a web management interface installed on top of Debian. It does not impose a storage model: you can use single disks, software RAID with mdadm or, through plugins, ZFS and disk-pooling solutions such as mergerfs combined with SnapRAID.
Characteristics:
- modest hardware requirements, it even runs on single-board computers;
- underneath is a normal Debian, so everything you know about Linux still applies;
- advanced features come from community plugins, with varying quality and maintenance;
- it needs a bit more manual work than the other two.
It is a good choice for limited hardware or for anyone who wants a light, transparent system.
Quick comparison
| Aspect | TrueNAS | Unraid | OpenMediaVault |
|---|---|---|---|
| Disk model | ZFS, vdevs | array with dedicated parity | your choice: mdadm, ZFS, mergerfs |
| Mixed disk sizes | poorly suited | yes | depends on the solution |
| Data integrity | very high | good, with per-disk file systems | depends on the solution |
| Licence | free | commercial | free |
| Minimum hardware | medium | medium | low |
| Apps and VMs | built in | built in, large catalogue | Docker via plugin |
How to choose
Three questions help more than any ranking:
- Are the disks all the same already, or will they arrive gradually? Matching disks bought together suit TrueNAS; mixed disks gathered over the years favour Unraid or mergerfs with SnapRAID.
- What kind of data will you store? Documents, databases and virtual machines benefit from ZFS. A media library that rarely changes fits well with separately calculated parity.
- Will the NAS also be the application server? If so, the app catalogue and VM management matter. If the homelab already has a hypervisor, the NAS can stick to storage, which is often the most robust setup.
In my work I prefer to keep roles separate when possible: the NAS keeps the data, the hypervisor runs the services. A problem with an application should not put the archive at risk.
Something none of them replaces
Redundancy and parity protect against a disk failure, not against accidental deletion, ransomware or a fire. Snapshots and replication help with the first two only if configured carefully; the third needs a copy in another place. Whatever system you choose, backup remains a separate project.
In short
- TrueNAS bets everything on ZFS and integrity, but requires planning the disks.
- Unraid accepts mixed disks and grows one disk at a time, with a paid licence.
- OpenMediaVault is light and flexible, built on Debian and plugins.
- The choice depends on how the disks arrive, the type of data and the NAS's role.
- No form of redundancy replaces an off-site backup.
