RAID-1 a couple of drives, and take backups. If the worst happens, you can restore offline from your backups. If you seriously need 100% uptime at home, in the face of multiple drive failures, you are doing something badly wrong. Or, at least, doing something far beyond 'home use'...
Many of us here work from home at times, either occasionally or regularly, and we have our own projects in addition to our day job. We each make our own decisions as to what configuration gives us the most acceptable level as performance given the level of risk we're willing to accept.
If a couple of drives in a RAID1 configuration works for you, great! It doesn't fit my needs since my media PC has about 20TB of usable space (~15TB in use) and I don't want to have to hunt through backups of any form when I want to watch or listen to something.
I also have a NAS for my more important files. It's backed up to a cloud provider as well, but the amount of time it would take to download everything after a failure would be very stressful for me, so I spent a bit of money up front for my setup. It's not 100% protection, but so far I've had two drives start to fail, but I was notified in plenty of time to get new drives in and let the array rebuild.
I'm happy with my setup. Well, happy based on the amount of money I was willing to put into it, obviously.
Either way, my setup isn't madness. It's simply different than what you do.
That's business use, it just happens to be at home. Home use is family-style, some documents and pictures, maybe some larger multimedia.
Backups are important, but not ever having to use them is even better.
Not only that, but having RAID or mirror sets gives you flexibility in ways that you might not think about up front. For instance, I just replaced some old 750GB disks with new 5TB disks. I added the new 5TBs to the the mirror set and let it bring all the data across automatically. When it was done, I dropped the 750s out and resized the raid set to use the whole 5TB (I told it it was already clean so it didn't have to sync up a bunch of unused space). Then, finally, I resized the filesystem that was mounted on that mirror set. This was all done live, with data actively being read and written to while all this volume manipulation stuff was happening.
That is why you use RAID at home (and lvm, too).
RAID preserves performance and/or uptime in the face of hardware failures. It does not protect against data corruption or deletion. It will happily sync those across all your disks.
Backups protect against any data loss: hardware, software, even intentional. The key feature of a backup is that it is insulated from live data operations (including RAID sync).
* Plug new hard drive in
* cp data on to new hard drive
IMO, much simpler, straightforward, less prone to errors and your data is perfectly safe until you do something with the old hard drive. Again, it's not 100% uptime but this is your home, not a mission-critical business.
And less error prone? Are you joking? In a non-mirror system you have to re-partition and set everything up the way it was, you have to really hope you copy things back correctly (do you have a bunch of hard links? Does cp copy them correctly? What's that option to rsync again? Do you have enough memory to copy hard links correctly? Are xattrs going to copy correctly?). Sigh. On top of that all you can't actually use that disk while any of this is happening. Grrr, and it's going to take 11 hours to copy 5 TB of data back (at 125MB/s)! If you're perfectly happy with your computer being out of commission for 11 hours, be my guest.
Also, when the old disk is removed from the mirror set, it's a complete image copy of the data. I'm not sure why you think that isn't the case...
Seriously, making every disk in your computer a mirror set is really a phenomenal idea. I've been doing it for years now and every time I have to upgrade or replace a disk it's made it heavenly. You shouldn't pooh pooh it until you've actually tried it.
In my experience, mirrored and/or striped-mirror type RAID implementations are more reliable, performant, and easier to maintain than any variation of parity RAID. Even for a home setup, it's just not worth my time.
A few years ago I built a home NAS. Back then, maximum drive sizes were 3TB for 3.5", and 1TB for 2.5". The tiny ITX case I had had one 3.5" slot, and one 5.25" slot.
So, I could either do a RAID1 with 2x3TB 3.5" disks; or get a 6x2.5" adapter for the 5.25" bay and do a RAID5/6 with 7x1TB for a net capacity of 5/6 TB.
I'm still not sure whether it was a good idea – the hardware looks a bit adventurous: http://dl.creshal.de/IMG_0873.JPG and was loud as hell –, but it worked well for about five years without any drive failures.
(Then I replaced it with a smaller NAS with 2x2TB drives in RAID, because as it turned out, my interests went from binge-watching storage intensive TV series to reading more books, and I never ended up using more than 1TB storage anyway.)
I'm going to hijack this thread slightly to ask: if I want to have a couple of RAID-1 drives running an open source NAS, what's the lowest power hardware solution with acceptable performance?
Depends what you define as acceptable. RAID-1 (as in mdadm) is fairly low on CPU requirements, generally something like an Intel atom chipset (late cedarview chipsets have a TDP around 6.5w) should give reasonable performance, otherwise a mobile/low end i3 would give even better performance.
Other than that, if you're not planning to exploit any of ZFS's functionality, and are looking to deploy on as cheap hardware as possible, mdadm RAID1 (with LVM over the top) is just the ticket. If you need to expand, just add another mirrored pair, assign it a physical volume, add that to the volume group, expand your logical volume, then expand your filesystem (ext4 supports online resize and is very stable, XFS is also a solid contender). All of this is fairly boring compared to ZFS, but it works and it works well..
Since there is a mirrored copy this a correct copy of your data but since there is no metadata or checksums, mdadm has no way to tell which is correct.
ZFS will silently detect the corruption and will rewrite the data restoring the duplicate copy of the data again.
All this works great without ECC RAM, recent studies of data corruption have shown that RAM is much more reliable then previously thought. ECCisnt needed for ZFS for home use.
It's not madness if you're backing up 2-4 home PCs either, storing your movie library. I know somebody that rips their blu-ray disc library to full 32gb video files. That's madness but it doesn't suprise me people do that though. Some of us are hoarders for data. Some people behave like they are the internet archive of the darknets too.