Helping people with computers... one answer at a time.
Hard drives fail, and external drives are no different. I'll look at the implications of external hard drive failure, and what you should do.
I've had two external hard drives fail in the past few months. One was an older drive that required external power in addition to a USB connection (to my Windows XP computer which has lots of RAM). The other was a newer, smaller one, just a year old, which was connected via USB alone. Is this kind of failure common? How do I make sure all my data is not at risk if I dispose of these? And will the new, larger capacity USB flash drives work as well for back-ups?
I'm not quite sure what "this kind of failure" might specifically refer to, but yes - drives do fail.
If you're asking about the timing - well, I've had two drives from the same manufacturer die within a few months of each other, and then had no failures for a couple of years.
My case is a little different than yours and I was able to draw a conclusion.
In your case my conclusions are little different.
My conclusion in your case?
Drives fail. Given that the drives are of different ages and different models, even though from the same manufacturer, I wouldn't read much more into it yet other than exactly that: drives fail.
That external drives might fail should be no surprise. They're just drives, after all, and occasionally even subject to slightly harder environments if they get carried, jostled or moved around a lot.
The take-away is actually very simple: back up. And yes, sometimes that means backing up your backup drive.
It all depends on how you backup.
The rule of thumb is very, very simple: if data exists in only one place, then it's not backed up. If that one place is your computer, you need to back it up. If that one place is an external drive, then you probably want to figure a way to back that up too. As you can see the external drive can die, and often without warning.
In my case, the two external drives I had fail were the exact same model, from the same manufacturer, purchased relatively close to each other. When both eventually ended up failing, the conclusion I drew was different: I chose to avoid that manufacturer for a while. (I say "a while" - typically meaning a couple of years - because disk manufacturer's quality ebbs and flows over time. I'd revisit them if their reputation improved someday.)
What to do when you dispose of a drive really depends on how sensitive the data is and how much effort you want to go through when you dispose of them.
Since they're external drives, it's possible that the failure is with the drive enclosure's circuitry and not the drive itself. If that's the case, you can actually remove the drive and potentially start using it elsewhere - in a machine perhaps - or connect it long enough to securely erase its contents.
If you can't regain access to the drive in some way then the only secure way to ensure the drive is no longer accessible to anyone - particularly someone motivated enough to take more extreme recovery methods - is to physically destroy the drive. Make sure that the drive's case is open, and the platters exposed and ideally damaged.
I've drilled holes in dead drives to achieve this effect.
I have mixed feelings about flash drives.
They're darned convenient, I'll give you that. In fact I carry one with me at all times.
However there are issues:
They wear out. Inexpensive ones more quickly than the more costly ones. A quality external flash drive of the capacity I suspect you might want could get quite pricey.
They're sometimes slower... reading from flash memory is typically quite fast, but writing is significantly slower - frequently much slower than an equivalent hard drive. (Mine most definitely are - even the more costly ones.)
Longevity isn't proven. This isn't about wearing out as much as it is about just retaining data. An unused hard drive will retain its data safely for years - a flash drive isn't as certain.
My take is that for backup and archiving you really want an actual hard drive. For data transfer, convenience and perhaps as a third level backup then flash drives may make sense.