Adding more disks to it. The thing is that disks used in RAIDs tend to be of the same model and even batch and thus suspicious to the same vulnerabilities. Home users typically don't really have neither the need of the capacity/speed nor the budget to allow enough disks in the RAID to allow two disks failing at the same time. As disks get larger and larger, it's really unlikely to have no defects for all disks during the expected life span of the RAID. If one disk in the array shows signs of failure, the others probably going to have the exact the save issue soon. Given the size of the disks, it can take days to rebuild the array after replacing a single failed disk. Making it worse, rebuilding itself also put more pressure on the remaining disks that might be imminent to fail and can really lead to a cascading failure of multiple disks, in which case, total loss of data is unavoidable.

So even my NAS supports RAID5/6, I still go with single disk volumes so that in event of disk failures I'll only have to replace the failed disks and lose only the data on it in the worse case. In fact, I don't lose much because my data does not have to be in the same volume and the disks are ready fast enough and made my home network the bottleneck.