My Current Backup Approach
Although I have used RAID 1 and RAID 10 in the past - even occasionally RAID 0, I am not currently using any of those approaches to maintain my backups. In fact, I don't even have a RAID setup in my current system even though it's perfectly capable of supporting one. I even have a pair of matched hard drives.
In my last several builds, I have switched from rotating hard disk drives (HDDs), to a combination of Solid State Drives (SSDs) and HDDs, and finally to just SSDs. In my current build, I'm using a pair of 2 TB NVMe SSDs that install directly on the motherboard. (The speeds on the two SSDs differ.) Even though the prices have come down dramatically, the cost of SSDs makes setting up a RAID a bit prohibitive. Instead, I have switched my desktop, a laptop, and a file server to using offsite backup over the Internet. I have used a couple of services to do that.
Nasty Note: 22 August 2017
CrashPlan has decided they no longer wish to service consumers. After five years of giving them more than I thought they were worth ... I am not pleased.
I very recently switched from CrashPlan Home (Family Plan) to IDrive. I didn't switch because I had any issues with CrashPlan. I switched because CrashPlan decided they no longer want to bother with consumers. Like CrashPlan, IDrive lets me pick the files and folders I want to back up. IDrive doesn't have unlimited storage as CrashPlan did. However, their $70/year plan - which is less than half what I was paying CrashPlan per year - includes up to 2TB of storage for an unlimited number of devices (where the list of devices includes iPhones and Android phones and tablets in addition to computers). That's considerably more space than I actually used with CrashPlan.
CrashPlan Home was available as both a free version and a subscription version. The free version of the software supported backing up to an external disk, another computer in your house or even a friend's computer. The free version did not support backing up to the Internet. With a yearly subscription on the CrashPlan for Home Family Plan, I could back up any 10 devices to both a local and CrashPlan's Internet-based servers (in parallel). None of the other online backup services (including IDrive) seems to support that parallel local/online backup. IDrive's (significantly more expensive) business plans offer Hybrid backup, which does support both.
IDrive allows anyone to create a free, small (5GB limit) online backup using their software. It also seems to support creating a local backup to an external or network drive (I haven't tried it.) IDrive does let me use my own encryption key and has 256-bit AES encryption. I can get at my backed-up files from anywhere (so long as I have the key with me). IDrive keeps files backed up to it forever or until cleaned up (i.e., manually deleted, but it has tools to help with that) and keeps the last 10 updates to any file. I'm not sure how IDrive tallies up disk usage, so it remains to be seen if this will become an issue or not.
Since the very first backup(s) can take excruciatingly long over slower Internet connections if the amount of data is moderately large, so IDrive offers IDrive Express that allows the user to use the IDrive software to backup to an external drive (which IDrive supplies). After that backup completes, the user ships the drive to IDrive (IDrive pays for the shipping), and they load the data onto their servers. This is known as a Seeded Backup. From that point, the users only need to do incremental backups. IDrive customers can use this service to bulk upload their data once per year for free. It's $60 for additional uploads. IDrive also supports loading backed-up data onto an external drive from their servers and shipping that to you in the event of a major loss of data. That costs $100 for each request. (CrashPlan originally offered the same services for home users but discontinued them.)