Just compare RAID to any other backup tool (online cloud, "realtime" file synchronization, etc.), and imagine a case where you are dealing with critical data being generated/processed at a high volume.
Which is exactly what makes it suitable and potentially necessary for enterprise environments and *not* for home users. How many home users do you know of that fit that criteria, "data being generated/processed at high volume"? I am one of the most demanding computer users I know and even I don't think RAID is worthwhile on my system, and I spent more than $3000 for it, so easily could have afforded it. If by "data" you're talking about lots of small files (e.g. you're a coder), then I'd still advocate a software solution in that case, because you can use a realtime local versioning system (*not* a DVCS), which accomplishes the same goal *and* improves your work by providing back versions.
Regarding backup "performance", yes CrashPlan uses a lot of memory on my system, but then it's also doing a lot more than a RAID solution would be (encryption, non-local backup, deduplication). If I turn off some of those advanced features, it's reasonable to think memory use will come down. Certainly there are lighter-weight backup (or, perhaps better yet, sync) solutions that are a more direct comparative to RAID, and while yes they inevitably have a greater performance impact than RAID, in practice it can and should be minimal. Even CrashPlan doesn't use much CPU at all, despite its high memory use.
Besides, would you not agree that RAID is *not* backup, and you'll need to be running backup software *anyway*?
Sometimes the greater the level of protection afforded, the greater the problems created should it ever fail.
Or as a friend of mine once put it: Slay one monster and it's only a matter of time before a bigger monster take its place.
(and other stuff 40hz said)
Yes, exactly. As I said, it's adding complexity, which I think most of us can agree is generally a bad word for the home user. Sure if things are working as expected, it provides benefit, but the moment something goes wrong, even the "planned for" disk failure, it starts to diverge significantly from the simplicity of the average data restore scenario. I suppose being able to replace (install) a failed hard drive should be a prerequisite for running a RAID, at the very least. But this is not necessarily as dead-simple as the average computer hardware jockey might think. If your RAID is not external, then you'd better hope you have your drives well labelled internally, because of course they're all identical. Sure, you can try to match the BIOS or Windows-recognized SATA port with the failing drive, but it's not necessarily trivial. And that can become an issue even in the "expected" failure scenario, nevermind the loss of the controller as others mentioned, or - god forbid - multi-drive corruption.
Rebuilding a RAID array does degrade performance to a mildly noticeable degree...but restoring from backup - especially an image backup - completely annihilates it. Progress and performance are both exactly zero as you sit about twiddling you thumbs waiting a few hours to get on with your life. And that's only after you get back from the hard drive store (with the replacement) which will hopefully still be open at whatever ungodly hour the thing decides to go poof at.
Unless you keep a spare drive around in the RAID scenario, you'll run in degraded mode until you replace the drive, which is riskier. You could keep a spare drive around for recovery in both scenarios. Also, RAID on the boot volume? Another complication. I was sort of assuming we're RAIDing our critical data store, and thus "full system image" backup isn't necessary. Use a simple sync "backup", your backup drive is then a 1:1 copy of your data, and you can just flip it over to primary if your main data store disk fails. In other words, the issues you point out - if they are even really issues for the home user - can be mostly dealt with using simple software and configuration strategies. That being said, I would still contend that downtime concerns of that significance are really fairly exclusive to enterprise use. After all, what home user can't just go out for a movie while their backup restores?
So, basically, RAID1 for supplementary backup purposes only, and to aid speed of recovery, *if* it's worth the cost and potential hassle to you. But frankly I just feel like it's a slippery slope to ever recommend RAID to any "home" user. The people barney is talking about sound more like IT professionals and potentially have the knowledge to deal with anything that would go wrong, so it's a lot more reasonable for them to make the (informed) choice to use it at home.