One of the biggest drawbacks to RAID, in my opinion, is that it requires all drives to be the same size. I had a wide range of storage drive sizes that I wanted to use for my NAS, including 3TB, 4TB, 6TB, and 8TB drives.Someone's working on improving this for ZFS, so might be history in the near future[1].
While TrueNAS (and other software-based RAID systems) can typically be “portable” in that you can move the OS (Operating System) to a new system and your data goes with it, that still makes you rely on that OS not to fail. The operating system has the information pertaining to what data goes on what drive, and that's the only way to access the data.
This is just wrong, at least for TrueNAS with ZFS. ZFS stores all the info it needs, redundantly, so all you need is some OS with a compatible ZFS version (same or higher), and you can mount the pool in that OS and access your data.
That said, I've come to the same conclusion that RAID >0 might not be as useful for home users and similar who don't have hard uptime requirements.
A simple striped pool can be easily built on mixed capacity drives, and one can achieve sufficient disaster mitigation by periodic sending of snapshots to another pool. Expanding the pool by replacing a single disk is a bit more time-consuming as you'd need to restore from backup, but is at least easy and beats having to upgrade multiple disks at once.
[1]: https://hexos.com/blog/introducing-zfs-anyraid-sponsored-by-...
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