all media is flawed all data is fragile...
we use hard drives, cards, flash drives, solid state media like it's going out of fashion at work we thrash'em and sell'em on after 6 months sometimes less, data is money to us so it's simple exconomics of scale.
for a private user
SD card's are very reliable for the money I'd dunked'em in salt water and they still worked, I don't recommend but it can be done. SXS drives are great but proper money £400 plus, DVD's as backup storage is very good in dark and temprature colded space. (shoe box under the bed) Hard drives can fail but we've only every had a few go really wrong.
Or external storage like BT vault, iron mountain, FTP sites, google mail etc. are all great till they crash, you forget your login or your money runs out.
I would say if it's important 3 copies is enough on two seperate mediums
and yes... Jobs a carrott....