NAS system: TrueNAS, Unraid or Synology?

Picking a NAS system feels like picking a starter Pokémon: you live with the choice for years, and swapping later costs a weekend and a full backup. So it pays to compare before the first disk is formatted.

The short answer

Which NAS system should you pick: TrueNAS, Unraid or Synology? It depends on four criteria, not on a brand. If you want a ready-made box with the least maintenance and can live with the vendor's drive rules, a Synology NAS with DSM fits. If you own disks of different sizes and want to add them one at a time, Unraid fits, and you pay a one-off licence. If you build your own hardware, buy matching disks and want ZFS with checksums and snapshots at no licence cost, TrueNAS Community Edition fits. All facts here are as of 25 Oct 2026 and come from iXsystems, Lime Technology (Unraid) and Synology. We name no NAS models and no hardware prices. And whatever you pick: RAID protects against a failed disk, not against deletion, ransomware or fire. You still need a backup.

How it works

1. Three different products. Synology sells hardware with its own operating system, DiskStation Manager (DSM). TrueNAS Community Edition and Unraid are operating systems that you install on your own x86 machine [2][7]. That one difference decides a lot: with Synology you choose a model and the vendor decides which drives, updates and support you get. With the other two you choose every part yourself and carry the responsibility for it.
2. Versions as of 25 Oct 2026. iXsystems recommends TrueNAS 25.10.7 (released 2 Sep 2026) for the "General" user type. 27.0.0-RC.1 from 6 Oct 2026 is an early release for testers [1][2]. The version that was called TrueNAS 26 during its beta is now named TrueNAS 27, and iXsystems moves to an annual release cycle with simple version numbers [3]. Lime Technology lists Unraid OS 7.3.4 from 22 Oct 2026 as the latest stable release and 7.4.0-rc.2 as a release candidate for test systems [9][10]. Synology's release notes show DSM 7.4.1-90080 from 23 Jul 2026, which has since received Update 1, and DSM 7.3.2-86009 Update 5 from 12 Oct 2026 for devices on the 7.3 line [16]. For a list of older models, Synology names DSM 7.4 as the last version they can upgrade to [16]. Check that list before you buy a used Synology.
3. How redundancy works. TrueNAS stores data in ZFS. A pool consists of vdevs (groups of disks), and each vdev carries its own redundancy. If one vdev fails, the whole pool is lost [15]. The classic Unraid array works differently: up to two dedicated parity disks protect data disks that each keep their own file system. Each parity disk must be at least as large as the largest data disk [12][13]. With XFS, the default, every data disk is a self-contained file system that any Linux system can read [14]. Our reading: if more disks fail than you have parity, you lose the content of the failed disks, not the content of the rest. Synology uses Synology Hybrid RAID (SHR), which is built on Linux RAID. SHR-1 survives one failed disk and SHR-2 two [20].
4. How you grow the storage. TrueNAS can extend a RAIDZ vdev one disk at a time. Data stays available during the expansion, and fault tolerance stays the same: a RAIDZ2 that grows from four to six disks still survives only two failures. Old blocks keep their old ratio of data to parity, so the vdev reports less capacity than a freshly built one [6]. Other options are a new vdev or replacing every disk with a bigger one [6]. In Unraid you add a disk of any size up to the size of your parity disk. Unraid clears (zeroes) the new disk first so parity stays valid [12]. SHR accepts added disks that are at least as large as the smallest disk in the pool [21]. When you replace disks, extra capacity stays unused until a second disk of the same size can pair with it [22].
5. Which drives you may use. TrueNAS publishes no list of approved drives. Its hardware guide warns against drive-managed and host-aware SMR drives and says host-managed SMR drives do not work with ZFS at all. It also discourages USB disks as primary storage [5]. Unraid lets you mix sizes; the parity rule from step 3 is the main limit [12]. Synology has tightened its rules for models from 2025 onwards. On the knowledge-base page, retrieved 25 Oct 2026, DS Plus and desktop FS models running DSM 7.3 or later accept hard disks and 2.5-inch SATA SSDs that are not on the compatibility list for new installations and storage pools. M.2 NVMe SSDs that are not on the list only work when you migrate them from another Synology. Rack (RS Plus), XS and other business series accept unlisted hard disks only for migration [17]. For Value and J series, the column for unlisted drives in that table is empty, although Synology's press release from 8 Oct 2025 named them among the series that support non-validated third-party drives [17][18]. The rules do not apply retroactively to models launched before 2025 [17]. Synology says third-party drives do not affect the warranty, but support cannot help with problems caused directly by those drives [19].
6. How much RAM. TrueNAS asks for 8 GB for basic operation with up to eight disks, plus 1 GB for every further disk, and more for apps, virtual machines and services such as directory integration. Deduplication needs about 5 GB per TB of storage [4]. On ECC memory (RAM that corrects bit errors), iXsystems sums up the debate: most users strongly recommend it, yet many TrueNAS systems run without it every day, and all RAM should be tested before use [4]. Unraid notes that ZFS pools need more RAM than Btrfs pools, without giving a number [13]. On a Synology, the model decides how much RAM is installed and how far you can upgrade.
7. What it costs. TrueNAS Community Edition is a free download [2]. Unraid sells perpetual licences: Starter for $49 (up to 6 storage devices), Unleashed for $109 (no device limit from the licence) and Lifetime for $249, prices from unraid.net, retrieved 25 Oct 2026 [7]. Starter and Unleashed include one year of updates. After that, an optional extension costs $36 per year. Without it you keep the software and still get patch releases for your minor version until that version reaches end of life. Lime Technology supports the two most recent minor versions [8]. If you boot from an internal SSD or NVMe drive, which Unraid supports since 7.3, those boot drives count towards the device limit, both of them in a mirror [11]. There is a free 30-day trial [8]. With Synology, the software is part of the hardware price. We did not check hardware prices.
8. How much maintenance. On TrueNAS you choose an update train. "General" is field-tested software, while early releases are for testing and feedback [1]. Unraid stops patching a minor version as soon as two newer minor versions are public, betas and release candidates included, so plan your licence extension or upgrade rhythm [8]. Synology rolls out DSM updates in stages, and older devices stop at a fixed version [16]. On all three systems, regular disk checks (scrub or parity check) and a restore test are part of the job.

The three systems by criterion (as of 25 Oct 2026)

A worked example with invented disks

This is a calculation, not a test. You already own two 8 TB and two 4 TB disks and want single redundancy (one disk may fail). We ignore file-system overhead and the difference between TB and TiB.

• Unraid: one 8 TB disk becomes parity. The data disks give 8 + 4 + 4 = 16 TB.
• SHR-1: SHR splits the disks into chunks. The first 4 TB of all four disks form one RAID 5 layer with 12 TB, and the remaining 4 TB on the two 8 TB disks form a mirror with 4 TB. Together that is 16 TB [20].
• TrueNAS, one RAIDZ1 vdev: the smallest disk sets the size of each member, so you get 3 x 4 = 12 TB. Two mirrors (8+8 and 4+4) also give 12 TB.

In this case Unraid and SHR use the existing disks better. ZFS would make sense if you buy matching disks anyway, or if checksums and snapshots across the whole pool matter more to you than the last 4 TB. If you later add a 12 TB disk, it would first have to become parity in Unraid, because parity must be at least as large as the largest data disk [12]. In SHR, the part of the 12 TB disk beyond the next-largest disk stays unused until a second disk of that size arrives [22]. In a RAIDZ1 vdev of 4 TB members, it contributes only 4 TB [6].

Checklist

• Write down how much capacity you need in three years and how many drive bays you have.
• Decide whether you want an appliance (Synology) or your own hardware (TrueNAS, Unraid).
• Check the release notes for the current version and the end of updates for your model.
• Check every drive against the vendor's rules: SMR type for ZFS, compatibility list and series for Synology.
• Calculate usable capacity and failure tolerance for your exact disks before you create the pool.
• Plan RAM by the vendor's numbers and test it before you store data.
• Read the Unraid licence terms if you choose Unraid, and note when your update year ends.
• Set up scrubs or parity checks and SMART monitoring.
• Set up a backup outside the NAS and test a restore before you trust the system.

Related pages: NAS explained; 3-2-1 backup and restore testing; ECC memory; ZFS: mirror or RAID-Z?; RAID-Z; Choosing NAS hard drives; SMR vs CMR.