The debate between Unraid and TrueNAS feels as strong as the debate between Plex and Jellyfin. The thing is, while Plex and Jellyfin solve a very similar problem, Unraid and TrueNAS aren't solving the same problem at all. In fact, they're very different at the core, so make sure you pick the right NAS OS for your specific use case.
TrueNAS wasn't always TrueNAS. TrueNAS actually got its start back in 2005 when the developer, Olivier, wanted to turn an old home PC into a NAS. He then built FreeNAS, which was later taken over by iXsystems in 2009 and introduced as TrueNAS as an enterprise appliance.
FreeNAS remained open and ran as a community version, but in 2019, iXsystems unified FreeNAS and TrueNAS under TrueNAS Community Edition and TrueNAS Enterprise.
The thing is, at this point, TrueNAS is built for enterprise, but it still works in a homelab situation. The backbone of TrueNAS is ZFS, which is a rock-solid file system that is perfect for enterprise use. With ZFS you create drive vdevs, which allow you to really have a very redundant system.
That's what TrueNAS is known for—redundancy. It's one of the most solid, reliable, and dependable NAS operating systems out there, for both home and enterprise applications.
However, ZFS is both TrueNAS' headlining feature and biggest downside. In fact, ZFS is the reason I chose not to use TrueNAS in my homelab back in 2021 when I first built it out.
ZFS functions much like traditional RAID, just with different names for the levels. RAIDZ1 is redundant to one drive failure, much like RAID 5 is. RAIDZ2 is redundant to two drive failures, much like RAID 6. However, ZFS also has RAIDZ3, which is redundant to three simultaneous drive failures.
The thing is, you can actually have multiple vdevs in a single drive pool. So, let's say you have six drives total, with three of them being 4TB and three being 8TB. With normal RAID, you would essentially have six 4TB drives if you put them into one normal RAID pool.
However, with ZFS, you could make a RAIDZ1 vdev of the three 4TB drives, and then another RAIDZ1 vdev of the three 8TB drives, and combine them into a big drive pool that was 24TB in size. This is something normal RAID isn't capable of.
So, TrueNAS really is built for enterprise-level functioning. It can handle hundreds of drives of any size, with all sorts of configurations, and remain rock solid through it all. But, it's pretty rigid in how it works. And that's why I personally chose to go with Unraid for my server back in 2021.
While TrueNAS is essentially infinitely scalable (so long as you can plug the drives into the main system), Unraid is not. Unraid only supports up to 30 drives in an array, and you can only have one array per server.
The array is the headlining feature of Unraid. Within an array, you can have basically any size drive you want and the array just adds it all up—outside of the one (or two) largest drives, those are reserved for parity.
So, if you have a big conglomerate of drives, like one 12TB drive, three 8TB drives, two 6TB drives, four 4TB drives, and two more 2TB drives, with TrueNAS and RAIDZ1, you actually could only use the 8TB and 4TB drives, as RAIDZ1 requires at least three drives to build the vdev.
Of course, you could choose to include the two 6TB drives with the 4TB drives, though you'd lose the extra 2TB of storage on each drive. The 2TB drives would basically be useless as a RAIDZ1 vdev, though they could be used as individual drives. Really, you would only get about 44TB of storage if you combined the 12TB with the three 8TB, and the two 6TB with the four 4TB drives.
Those same drives in Unraid, however, would give you 56TB of storage with the 12TB acting as parity. Need more storage? Pull out a 2TB and replace it with a 12TB, now you just gained another 10TB of storage.
