I haven’t seen any deleterious effects from what you’re proposing and I haven’t heard of any either. Were it me, I’d go for it.
this post was submitted on 21 Aug 2023
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Agreed. It’s not a safety issue it just won’t use the full drives capacity until they replace the other smaller drives
I run my Truenas Scale with 5 mirror vdevs. This is sort of like raid 10 (I don't need the differences explained to me). This means that I get 50% of the raw storage as usable but, it means that to upgrade space, I only need to upgrade two drives at a time. It also means that replacing a failed drive is fast, much faster than replacing a drive from a raidz* vdev. As you move to Truenas, this is something to consider. Given that you're going to have 4 drives total, I don't think you'd be wasting any additional space as you shouldn't consider raidz safe (same problem as raid 5, high risk of second drive failure during rebuild) which leaves you at raidz2.
Not an expert, but as far as I know running with mismatched drives isn't bad - it's just a pointless long-term configuration.
Are you planning on mirroring the drives? If you upgrade to 4 drives in the future you could just do 2 mirror vdevs with mismatched drive sizes per vdev. Also I'm surprised you're bothering with 6TB drives - you can get 14TB very cheap nowadays (recertified).
I looked at doing two vdevs but was put off by the lower usable storage. At a certain point, maybe that's not as important as I think though.
Yeah, the choice for 6TB wasn't my best. I got the two older drives a few years back on a Newegg flash sale, and it seemed like plenty, especially considering Unraid's model of 1 parity drive and 100% usable storage on the data drive(s). Then, when I decided to upgrade, I was too cheap to go buy 4 whole new drives, so I just went with more of what I already had (to add insult to injury, they're all WD Red drives...).
Yeah lower usable storage sucks, but it's an okay trade at the moment given its flexibility. raidz expansion is always "right around the corner" but never actually arrives - if it's merged a raidz array might make more sense for a smaller NAS.
Personally I've found that if you're really budget-conscious or have a low number of disks, MergerFS+SnapRAID backed by BTRFS disks is a better choice for flexibility (very similar to an Unraid setup), since you can add/remove at any time, and they can be mismatched drive sizes.
I have mismatched drives. Mostly 8TB, and 2 10TB. The 10TB are simply wasted money, but no other downsides.