I used to run raid 6 with traditional $1800.00 raid controllers. This limited my flexibility with upgrading drives. I would have to upgrade entire arrays after copying all of my data off somewhere ( part of the reason I have multiple arrays ). I have never lost more than one drive at a time, yes it did give a little more peace of mind during a rebuild after a drive failure running raid 6. But then again with unRaid if I did experience a multi drive failure my risk is still mitigated, as only the data on the failed drives is lost.
In my application (digital hoarder, I am trying to get help) I just want large amounts of protected space. I am not concerned with iops or being able to write to the array at over 300MB/s. I do have different classes of data, with a small subset of data I really care about. Some of this is actually copied across all three arrays, as well as on an off site server. An example of such data is family pictures and some (in my opinion, or my wife's) really important documents.
With my experience, I have a very important rule I live by for data.
If you have data you care about it needs to be in more than one place, a single disk, raid array, or physical location does not qualify.
Charles.