You probably meant striped.
In the thread I quoted myself from, I talk about the redundancy of RAID 10 VS RAIDZ1 VS RAIDZ2. Here you go:
Yes, 24 or 36 would be more ideal when using ZFS.
However, here’s something else to consider: Cold swap drives that wait for use.
What I mean is, pretend you still used the 20 drive chassis. Instead of using all 20 drives, use 16 and have 4 turned off, but in their bays.
Presuming you have some remote ability to manage the server, if you have a drive failure, you can remove that failed drive from the array, turn one of the unused drives on, then add it to the array and have it resilver.
This means you could repair RAID failures remotely, and just go replace the failed drive when you feel like it.
Four drives sitting there doing nothing is a bit significant though, so I can see why you may wish to not do that. However, another thing to consider is that 4 drives is the minimum RAID 10 number.
So you could have a second array for whatever reason. Performance or otherwise.
These are just ideas, but if I were you and I wanted max capacity, I would go for 24 or 36 to maximize capacity and efficiency.
What is the Mean Time Between Failure for the drives you intend to use? What are their URE specifications?
These two things along with their capacity should give you all the needed info to use the online calculators that exist specifically for calculating the odds of a RAID array failing.
IMO, even with 20 drives, 2 drives failing is very unlikely. Unlikely enough that I personally would trust that array to not lose my data.
HOWEVER, you should note in my above quote, when I mention “two drives failing”, I’m talking about a RAID 10 with 4 drives.
With RAIDZ1 and RAIDZ2, the more drives you use, the more capacity efficiency you get. With RAID 10, you’ll always get 50% capacity efficiency.
This means that yes, you sacrifice half your storage, but you also get a lot more potential redundancy.
What do I mean by potential redundancy?
You have 20 drives. A RAID 10 is a RAID 1 of a RAID 0 (or vice versa but this way is simpler to setup). So you have a RAID 0 of 10 drives, and a RAID 1 of that RAID 0.
If you lose 2 drives, one from each RAID 0, you lose your data.
If you lose 10 drives from one of the RAID 0’s, you lose no data.
You can see how that can be a blessing and a curse. So that’s not exactly ideal, because while it gives you the possibility of huge redundancy, the lower bound is 2 and that means this is a bit better than RAIDZ1 but a bit worse than RAIDZ2 (as my quote above talks about).
I actually have a question for you. What are the options for increasing RAID 10 redundancy when you have this many disks? I’m trying to consider if there’s a way to reasonably setup the RAID such that redundancy is >=2 disks without losing space. I don’t think that’s possible however.
Still, kad, it all depends how likely you think 2 disk failures is. I think it’d be low enough to not worry about, and even if it does happen, you have a 50% to not lose your data anyway.
Up to you.