RAID 1 vs data corruption

I am completely paranoid about backing up my data. I have a NAS server with a pair of hard drives in a RAID 1 array. I use software RAID to be independent of the hardware and I monitor the SMART reports of my drives regularly. So I thought that I was doing everything right and therefore that my NAS was bulletproof. But with three of my drives failing in the past 5 months, I started to question that assumption. So far I have been lucky that I never had two drives fail at the same time. I knew this was a risk but it seemed very unlikely. Now I am not so sure.

There is something else that I realized. What if one of my drives starts failing and makes mistake while writing my data. If the issue is reported by SMART, the drive will be taken offline automatically. But if the problem goes unnoticed, you end up with two drives with contradicting data. How can you tell which drive is correct. If you had three drives and one misbehaving, you could look at which two drives agree on the data and assume that they are the right ones. But with two drives, there is no way to tell!

So far RAID 1 saved my bacon. But it's not good enought. I need to find a contingency plan.

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