40 drives ? Why that is a huge amount of power , what is your space target
RAID 1 ? With 40 drives ? That would be absolutely stupid you want to use RAID 6 or 10 so you don’t waist 50 % of your space with RAID 1. Or some other N+2 disk redundancy.
Have you considered how much power such a large setup will need?
I'll have to watch a video on it later, I assumed having a 1:1 backup was the most efficient backup method possible without compression. I don't plan on utilizing every drive at once, and I don't plan on having more than 20 to start with, but it won't be much more than I already have, so I should be okay to start. I just want to make sure there room for expansion in the future. I don't need all 40 immediately. My UPS will tell me how much power I'm drawing, right?
You need to research raid 1,6,10 and zfs first. Make an informed decision and go from there. You're basing the number of drives off of (uninformed) assumptions and that's going to drive all of your decisions the wrong way. Start with figuring out your target storage amount and how many drive failures you can tolerate.
Skip ZFS unless you’re planning to get all 40 drives up front, which is pretty bonkers for a home server setup. Acquiring 40 drives incrementally and you’ll be hit with the hidden cost of ZFS.
That's definitely something to be aware of, but the vdev expansion feature was mergered and will be released probably this year.
Additionally, it looks like the authors main gripe is the current way to expand is to add more vdevs. If you plan this out ahead of time then adding more vdevs incrementally isn't an issue, you just need to buy enough drives for a vdev. In homelab use this might an issue, but if OP is planning on a 40 drive setup then needing to buy drives in groups of 2-3 instead of individually shouldn't be a huge deal.
I think the biggest issue home users will run into (until the finally merged PR gets released later this year) is that as they acquire more drives, compared to a traditional RAID cluster that they could expand, they’re going to see more and more drives proportions being used for parity. Once vdev expansion is possible, the system would be a lot more approachable for home users who doesn’t acquire all the drives up front.
Having said that, this is probably a lot less of a concern for someone intending to setup 40 drives in RAID1, as they’re already ready to use half of it for redundancy…