Thanks for all the info.
Yes, I have a very specific purpose in mind. Currently, I have a 4TB WD Red drive on my Intel i7 Manjaro KDE desktop, exclusively dedicated to store personal data, to include scanned records going back decades, some music (my CD collection converted to FLAC), etc., taking up at this point nearly 50% of said drive. I actually have two identical 4TB drives, one of them set up to automatically mirror the other, so I do not lose my data to an accidental HDD failure. Now that I am retired, I am about to start scanning negatives, slides and photos going back to my childhood, and this is likely going to take a monstrous amount of storage, especially if I select a higher resolution scanning on my Epson V600 scanner setting for this job, so, I figure a couple of 12TB HDDs in the same configuration as the 4TBs I now have would future-proof my storage needs for a LONG time to come, probably for whatever years I have left.
Thanks again.
Excellent,
Since you're already set with a good file system (though I would suggest looking into implementation of ZFS file system, it can be added to your OS, to have a checksum and self healing structure built for integrity). Even with out that, you're already in good shape having a mirror of your data, and not just parity (RAID, etc). Mirrors with big drives are better in general than smaller drives in a parity setup. Recovery is much more reliable, faster and frankly easier.
What you're describing is a drive that will receive data, and mostly simply have data read from it, no intense writes, re-writes, etc. Just a storage drive that is accessed but not re-using sectors over and over as you change data, your data is going to be static and merely add new data to new sectors over time. So basically what I'm saying is that you don't even need an enterprise or NAS class drive for this. Especially since you are mirroring. Sure they are better, but what they are better at is basically a lot of the stuff you won't be using them for. So for cost, you could be comfortable with desktop class drives as mirrors. They are simply accessed and read from.
The 12~14 TB drives are pretty good in terms of cost/capacity from either manufacturer right now. The 16Gb+ ones are still premium for cost in general. If you want to look into getting the most capacity for your money, take a look at shucking external HDD's. You can get 14TB WD Easystore drives from BestBuy for about $215 a piece ($250 after taxes, shipping, etc likely). The drives inside are good, white label drives that have their serial numbers akin to Ultrastar class drives. If that's not something you're interested in, and you want new retail off the shelf internal drives, by all means, whatever is affordable will do the job. I would not worry too much since you are mirroring and the idea that both drives will fail together or corrupt together is so minute that spending a lot more for better drives really doesn't drive that percentage chance anywhere meaningful. You could do fine with some Seagate Baracudas, or WD NAS class drives. Redundancy is worth a lot more than just better drives. All enterprise class drives will fail eventually. But several mirrored drives will outlast that even. I would target an enterprise class drive for something that needs to write, re-write, delete, write, re-write, expand, etc, like an operating system drive or a working environment drive. Drives that will simply be written to one time for the data set, occupy those sectors indefinitely, and simply add new data each time, and 99% of its life it's merely read-from can be virtually any drive that turns on, and safe with redundancy.
For critical storage, burn your most important documents, images, etc, to archival class optical media. It's the most affordable and will last beyond our life time (Bluray archival, DVD archival, M-Disc, etc).
Very best,