1). Understood, and it still makes no sense except for bulk storage. Even the crappiest TLC drive will be demonstrably better in every normal operation than any reasonable number of drives in a RAID 10 array.
Yeah, I'd be happy with a 2TB SSD if the cost was just 3x as much as the 2TB HDD. But it isn't, it's more like the cost of the computer I'd put it in.
And, more broadly speaking, most of what I use is bulk storage anyway. If it isn't, usually it'll fit on one of the >250GB SSDs.
3). Not only do I disagree with the premise that HDDs don't fail quickly or without warning; data recovery on either is far more expensive than you're implying. If software can fix it, the drive didn't really die. SSDs, in general, are far more reliable. Further, you should *never* have your data in a single place on a single drive. That's lunacy.
Yeah, agreed. Actually, to my recollection the last two HDD failures I had were abrupt and total: The drives were dead, unrecognized by anything. The solution of "plug into USB dock and attach to another computer" does not help for serious drive failure as you say, for dying drives it might just give you chance to get something off a volume that is now otherwise unbootable: The drive isn't going to get any better.
I have experience with HDD recovery firms: It's thousands to tens of thousands of dollars and there is no guarantee they'll be able to get anything. Generally they give you a preview of what your car purchase price will be buying you(i.e. they already did it and are holding your data contractually hostage), because what they can recover may not even be what you want.
Effectively, for the hobbyist, this is not a real option.
Backups people, your future self will thank you.
What application on a standard desktop needs sequential write speeds to be super high (well, ~200 MB/s, since that's all a 4-drive RAID 10 will do in practice)?
It really gets to the point for hobbyists where it's more like ~110MB/s, because unless you are doing a copy internal to that computer, you're going to need > 1Gbe to do anything better (which most hobbyists don't even have, save the turbonerds spending multiple thousands at STH etc...). Which is precisely why I got those cheapy 10Gbe Mellanox adapters: My drives were faster than what I could write to them (and that was *with* a completely dedicated p2p 1Gbe link).
And we're talking about "copy", not really an "application" per se, like you say.